diff --git a/guix/import/go.scm b/guix/import/go.scm
index 24d12acd97..a6e2af215f 100644
--- a/guix/import/go.scm
+++ b/guix/import/go.scm
@@ -5,7 +5,7 @@
 ;;; Copyright © 2021 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 ;;; Copyright © 2021 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
-;; Copyright © 2021 Sarah Morgensen <iskarian@mgsn.dev>
+;;; Copyright © 2021 Sarah Morgensen <iskarian@mgsn.dev>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -41,6 +41,7 @@
   #:autoload   (guix base32) (bytevector->nix-base32-string)
   #:autoload   (guix build utils) (mkdir-p)
   #:use-module (ice-9 match)
+  #:use-module (ice-9 peg)
   #:use-module (ice-9 rdelim)
   #:use-module (ice-9 receive)
   #:use-module (ice-9 regex)
@@ -244,129 +245,139 @@ and VERSION and return an input port."
                      (go-path-escape version))))
     (http-fetch* url)))
 
-(define %go.mod-require-directive-rx
-  ;; A line in a require directive is composed of a module path and
-  ;; a version separated by whitespace and an optionnal '//' comment at
-  ;; the end.
-  (make-regexp
-   (string-append
-    "^[[:blank:]]*([^[:blank:]]+)[[:blank:]]+" ;the module path
-    "([^[:blank:]]+)"                          ;the version
-    "([[:blank:]]+//.*)?")))                   ;an optional comment
-
-(define %go.mod-replace-directive-rx
-  ;; ReplaceSpec = ModulePath [ Version ] "=>" FilePath newline
-  ;;             | ModulePath [ Version ] "=>" ModulePath Version newline .
-  (make-regexp
-   (string-append
-    "([^[:blank:]]+)"                   ;the module path
-    "([[:blank:]]+([^[:blank:]]+))?"    ;optional version
-    "[[:blank:]]+=>[[:blank:]]+"
-    "([^[:blank:]]+)"                   ;the file or module path
-    "([[:blank:]]+([^[:blank:]]+))?"))) ;the version (if a module path)
 
 (define (parse-go.mod content)
-  "Parse the go.mod file CONTENT, returning a list of requirements."
-  ;; We parse only a subset of https://golang.org/ref/mod#go-mod-file-grammar
-  ;; which we think necessary for our use case.
-  (define (toplevel requirements replaced)
-    "This is the main parser.  The results are accumulated in THE REQUIREMENTS
-and REPLACED lists."
-    (let ((line (read-line)))
-      (cond
-       ((eof-object? line)
-        ;; parsing ended, give back the result
-        (values requirements replaced))
-       ((string=? line "require (")
-        ;; a require block begins, delegate parsing to IN-REQUIRE
-        (in-require requirements replaced))
-       ((string=? line "replace (")
-        ;; a replace block begins, delegate parsing to IN-REPLACE
-        (in-replace requirements replaced))
-       ((string-prefix? "require " line)
-        ;; a require directive by itself
-        (let* ((stripped-line (string-drop line 8)))
-          (call-with-values
-              (lambda ()
-                (require-directive requirements replaced stripped-line))
-            toplevel)))
-       ((string-prefix? "replace " line)
-        ;; a replace directive by itself
-        (let* ((stripped-line (string-drop line 8)))
-          (call-with-values
-              (lambda ()
-                (replace-directive requirements replaced stripped-line))
-            toplevel)))
-       (#t
-        ;; unrecognised line, ignore silently
-        (toplevel requirements replaced)))))
+  "Parse the go.mod file CONTENT, returning a list of directives, comments,
+and unknown lines.  Each sublist begins with a symbol (go, module, require,
+replace, exclude, retract, comment, or unknown) and is followed by one or more
+sublists.  Each sublist begins with a symbol (module-path, version, file-path,
+comment, or unknown) and is followed by the indicated data."
+  ;; https://golang.org/ref/mod#go-mod-file-grammar
+  (define-peg-pattern NL none "\n")
+  (define-peg-pattern WS none (or " " "\t" "\r"))
+  (define-peg-pattern => none (and (* WS) "=>"))
+  (define-peg-pattern punctuation none (or "," "=>" "[" "]" "(" ")"))
+  (define-peg-pattern comment all
+    (and (ignore "//") (* WS) (* (and (not-followed-by NL) peg-any))))
+  (define-peg-pattern EOL body (and (* WS) (? comment) NL))
+  (define-peg-pattern block-start none (and (* WS) "(" EOL))
+  (define-peg-pattern block-end none (and (* WS) ")" EOL))
+  (define-peg-pattern any-line body
+    (and (* WS) (* (and (not-followed-by NL) peg-any)) EOL))
 
-  (define (in-require requirements replaced)
-    (let ((line (read-line)))
-      (cond
-       ((eof-object? line)
-        ;; this should never happen here but we ignore silently
-        (values requirements replaced))
-       ((string=? line ")")
-        ;; end of block, coming back to toplevel
-        (toplevel requirements replaced))
-       (#t
-        (call-with-values (lambda ()
-                            (require-directive requirements replaced line))
-          in-require)))))
+  ;; Strings and identifiers
+  (define-peg-pattern identifier body
+    (+ (and (not-followed-by (or NL WS punctuation)) peg-any)))
+  (define-peg-pattern string-raw body
+     (and (ignore "`") (+ (and (not-followed-by "`") peg-any)) (ignore "`")))
+  (define-peg-pattern string-quoted body
+    (and (ignore "\"")
+         (+ (or (and (ignore "\\") peg-any)
+                (and (not-followed-by "\"") peg-any)))
+         (ignore "\"")))
+  (define-peg-pattern string-or-ident body
+    (and (* WS) (or string-raw string-quoted identifier)))
 
-  (define (in-replace requirements replaced)
-    (let ((line (read-line)))
-      (cond
-       ((eof-object? line)
-        ;; this should never happen here but we ignore silently
-        (values requirements replaced))
-       ((string=? line ")")
-        ;; end of block, coming back to toplevel
-        (toplevel requirements replaced))
-       (#t
-        (call-with-values (lambda ()
-                            (replace-directive requirements replaced line))
-          in-replace)))))
+  (define-peg-pattern version all string-or-ident)
+  (define-peg-pattern module-path all string-or-ident)
+  (define-peg-pattern file-path all string-or-ident)
 
-  (define (replace-directive requirements replaced line)
-    "Extract replaced modules and new requirements from the replace directive
-in LINE and add them to the REQUIREMENTS and REPLACED lists."
-    (let* ((rx-match (regexp-exec %go.mod-replace-directive-rx line))
-           (module-path (match:substring rx-match 1))
-           (version (match:substring rx-match 3))
-           (new-module-path (match:substring rx-match 4))
-           (new-version (match:substring rx-match 6))
-           (new-replaced (cons (list module-path version) replaced))
-           (new-requirements
-            (if (string-match "^\\.?\\./" new-module-path)
-                requirements
-                (cons (list new-module-path new-version) requirements))))
-      (values new-requirements new-replaced)))
+  ;; Non-directive lines
+  (define-peg-pattern unknown all any-line)
+  (define-peg-pattern block-line body
+    (or EOL (and (not-followed-by block-end) unknown)))
 
-  (define (require-directive requirements replaced line)
-    "Extract requirement from LINE and augment the REQUIREMENTS and REPLACED
-lists."
-    (let* ((rx-match (regexp-exec %go.mod-require-directive-rx line))
-           (module-path (match:substring rx-match 1))
-           ;; Double-quoted strings were seen in the wild without escape
-           ;; sequences; trim the quotes to be on the safe side.
-           (module-path (string-trim-both module-path #\"))
-           (version (match:substring rx-match 2)))
-      (values (cons (list module-path version) requirements) replaced)))
+  ;; GoDirective = "go" GoVersion newline .
+  (define-peg-pattern go all (and (ignore "go") version EOL))
 
-  (with-input-from-string content
-    (lambda ()
-      (receive (requirements replaced)
-          (toplevel '() '())
-        ;; At last remove the replaced modules from the requirements list.
-        (remove (lambda (r)
-                  (assoc (car r) replaced))
-                requirements)))))
+  ;; ModuleDirective = "module" ( ModulePath | "(" newline ModulePath newline ")" ) newline .
+  (define-peg-pattern module all
+    (and (ignore "module") (or (and block-start module-path EOL block-end)
+                               (and module-path EOL))))
+
+  ;; The following directives may all be used solo or in a block
+  ;; RequireSpec = ModulePath Version newline .
+  (define-peg-pattern require all (and module-path version EOL))
+  (define-peg-pattern require-top body
+    (and (ignore "require")
+         (or (and block-start (* (or require block-line)) block-end) require)))
+
+  ;; ExcludeSpec = ModulePath Version newline .
+  (define-peg-pattern exclude all (and module-path version EOL))
+  (define-peg-pattern exclude-top body
+    (and (ignore "exclude")
+         (or (and block-start (* (or exclude block-line)) block-end) exclude)))
+
+  ;; ReplaceSpec = ModulePath [ Version ] "=>" FilePath newline
+  ;;             | ModulePath [ Version ] "=>" ModulePath Version newline .
+  (define-peg-pattern original all (or (and module-path version) module-path))
+  (define-peg-pattern with all (or (and module-path version) file-path))
+  (define-peg-pattern replace all (and original => with EOL))
+  (define-peg-pattern replace-top body
+    (and (ignore "replace") 
+         (or (and block-start (* (or replace block-line)) block-end) replace)))
+
+  ;; RetractSpec = ( Version | "[" Version "," Version "]" ) newline .
+  (define-peg-pattern range all
+    (and (* WS) (ignore "[") version
+         (* WS) (ignore ",") version (* WS) (ignore "]")))
+  (define-peg-pattern retract all (and (or range version) EOL))
+  (define-peg-pattern retract-top body
+    (and (ignore "retract")
+         (or (and block-start (* (or retract block-line)) block-end) retract)))
+
+  (define-peg-pattern go-mod body
+    (* (and (* WS) (or go module require-top exclude-top replace-top
+                       retract-top EOL unknown))))
+
+  (let ((tree (peg:tree (match-pattern go-mod content)))
+        (keywords '(go module require replace exclude retract comment unknown)))
+    (keyword-flatten keywords tree)))
 
 ;; Prevent inlining of this procedure, which is accessed by unit tests.
 (set! parse-go.mod parse-go.mod)
 
+(define (go.mod-directives go.mod directive)
+  "Return the list of top-level directive bodies in GO.MOD matching the symbol
+DIRECTIVE."
+  (filter-map (match-lambda
+                (((? (cut eq? <> directive) head) . rest) rest)
+                (_ #f))
+              go.mod))
+
+(define (go.mod-requirements go.mod)
+  "Compute and return the list of requirements specified by GO.MOD."
+  (define (replace directive requirements)
+    (define (maybe-replace module-path new-requirement)
+      ;; Do not allow version updates for indirect dependencies (see:
+      ;; https://golang.org/ref/mod#go-mod-file-replace).
+      (if (and (equal? module-path (first new-requirement))
+               (not (assoc-ref requirements module-path)))
+          requirements
+          (cons new-requirement (alist-delete module-path requirements))))
+
+    (match directive
+      ((('original ('module-path module-path) . _) with . _)
+       (match with
+         (('with ('file-path _) . _)
+          (alist-delete module-path requirements))
+         (('with ('module-path new-module-path) ('version new-version) . _)
+          (maybe-replace module-path
+                         (list new-module-path new-version)))))))
+
+  (define (require directive requirements)
+    (match directive
+      ((('module-path module-path) ('version version) . _)
+       (cons (list module-path version) requirements))))
+
+  (let* ((requires (go.mod-directives go.mod 'require))
+         (replaces (go.mod-directives go.mod 'replace))
+         (requirements (fold require '() requires)))
+    (fold replace requirements replaces)))
+
+;; Prevent inlining of this procedure, which is accessed by unit tests.
+(set! go.mod-requirements go.mod-requirements)
+
 (define-record-type <vcs>
   (%make-vcs url-prefix root-regex type)
   vcs?
@@ -592,7 +603,7 @@ When VERSION is unspecified, the latest version available is used."
 hint: use one of the following available versions ~a\n"
                              version* available-versions))))
          (content (fetch-go.mod goproxy module-path version*))
-         (dependencies+versions (parse-go.mod content))
+         (dependencies+versions (go.mod-requirements (parse-go.mod content)))
          (dependencies (if pin-versions?
                            dependencies+versions
                            (map car dependencies+versions)))
diff --git a/tests/go.scm b/tests/go.scm
index 2dfdc97eb5..6749f4585f 100644
--- a/tests/go.scm
+++ b/tests/go.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2021 François Joulaud <francois.joulaud@radiofrance.com>
+;;; Copyright © 2021 Sarah Morgensen <iskarian@mgsn.dev>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -31,6 +32,9 @@
   #:use-module (srfi srfi-64)
   #:use-module (web response))
 
+(define go.mod-requirements
+  (@@ (guix import go) go.mod-requirements))
+
 (define parse-go.mod
   (@@ (guix import go) parse-go.mod))
 
@@ -95,6 +99,41 @@ replace (
 
 ")
 
+(define fixture-go-mod-unparseable
+  "module my/thing
+go 1.12 // avoid feature X
+require other/thing v1.0.2
+// Security issue: CVE-XXXXX
+exclude old/thing v1.2.3
+new-directive another/thing yet-another/thing
+replace (
+        bad/thing v1.4.5 => good/thing v1.4.5
+        // Unparseable
+        bad/thing [v1.4.5, v1.9.7] => good/thing v2.0.0
+)
+")
+
+(define fixture-go-mod-retract
+  "retract v0.9.1
+
+retract (
+	v1.9.2
+	[v1.0.0, v1.7.9]
+)
+")
+
+(define fixture-go-mod-strings
+  "require `example.com/\"some-repo\"` v1.9.3
+require (
+        `example.com/\"another.repo\"` v1.0.0
+        \"example.com/special!repo\" v9.3.1
+)
+replace \"example.com/\\\"some-repo\\\"\" => `launchpad.net/some-repo` v1.9.3
+replace (
+        \"example.com/\\\"another.repo\\\"\" => launchpad.net/another-repo v1.0.0
+)
+")
+
 (define fixtures-go-check-test
   (let ((version
            "{\"Version\":\"v0.0.0-20201130134442-10cb98267c6c\",\"Time\":\"2020-11-30T13:44:42Z\"}")
@@ -178,7 +217,7 @@ require github.com/kr/pretty v0.2.1
     (string<? (car p1) (car p2)))
   (test-equal name
     (sort expected inf?)
-    (sort ((@@ (guix import go) parse-go.mod) input) inf?)))
+    (sort (go.mod-requirements (parse-go.mod input)) inf?)))
 
 (testing-parse-mod "parse-go.mod-simple"
                    '(("good/thing" "v1.4.5")
@@ -214,6 +253,98 @@ require github.com/kr/pretty v0.2.1
    ("github.com/go-check/check" "v0.0.0-20140225173054-eb6ee6f84d0a"))
  fixture-go-mod-complete)
 
+(test-equal "parse-go.mod: simple"
+  `((module (module-path "my/thing"))
+    (go (version "1.12"))
+    (require (module-path "other/thing") (version "v1.0.2"))
+    (require (module-path "new/thing/v2") (version "v2.3.4"))
+    (exclude (module-path "old/thing") (version "v1.2.3"))
+    (replace (original (module-path "bad/thing") (version "v1.4.5"))
+      (with (module-path "good/thing") (version "v1.4.5"))))
+  (parse-go.mod fixture-go-mod-simple))
+
+(test-equal "parse-go.mod: comments and unparseable lines"
+  `((module (module-path "my/thing"))
+    (go (version "1.12") (comment "avoid feature X"))
+    (require (module-path "other/thing") (version "v1.0.2"))
+    (comment "Security issue: CVE-XXXXX")
+    (exclude (module-path "old/thing") (version "v1.2.3"))
+    (unknown "new-directive another/thing yet-another/thing")
+    (replace (original (module-path "bad/thing") (version "v1.4.5"))
+      (with (module-path "good/thing") (version "v1.4.5")))
+    (comment "Unparseable")
+    (unknown "bad/thing [v1.4.5, v1.9.7] => good/thing v2.0.0"))
+  (parse-go.mod fixture-go-mod-unparseable))
+
+(test-equal "parse-go.mod: retract"
+  `((retract (version "v0.9.1"))
+    (retract (version "v1.9.2"))
+    (retract (range (version "v1.0.0") (version "v1.7.9"))))
+  (parse-go.mod fixture-go-mod-retract))
+
+(test-equal "parse-go.mod: raw strings and quoted strings"
+  `((require (module-path "example.com/\"some-repo\"") (version "v1.9.3"))
+    (require (module-path "example.com/\"another.repo\"") (version "v1.0.0"))
+    (require (module-path "example.com/special!repo") (version "v9.3.1"))
+    (replace (original (module-path "example.com/\"some-repo\""))
+      (with (module-path "launchpad.net/some-repo") (version "v1.9.3")))
+    (replace (original (module-path "example.com/\"another.repo\""))
+      (with (module-path "launchpad.net/another-repo") (version "v1.0.0"))))
+  (parse-go.mod fixture-go-mod-strings))
+
+(test-equal "parse-go.mod: complete"
+  `((module (module-path "M"))
+    (go (version "1.13"))
+    (replace (original (module-path "github.com/myname/myproject/myapi"))
+      (with (file-path "./api")))
+    (replace (original (module-path "github.com/mymname/myproject/thissdk"))
+      (with (file-path "../sdk")))
+    (replace (original (module-path "launchpad.net/gocheck"))
+      (with (module-path "github.com/go-check/check")
+            (version "v0.0.0-20140225173054-eb6ee6f84d0a")))
+    (require (module-path "github.com/user/project")
+             (version "v1.1.11"))
+    (require (module-path "github.com/user/project/sub/directory")
+             (version "v1.1.12"))
+    (require (module-path "bitbucket.org/user/project")
+             (version "v1.11.20"))
+    (require (module-path "bitbucket.org/user/project/sub/directory")
+             (version "v1.11.21"))
+    (require (module-path "launchpad.net/project")
+             (version "v1.1.13"))
+    (require (module-path "launchpad.net/project/series")
+             (version "v1.1.14"))
+    (require (module-path "launchpad.net/project/series/sub/directory")
+             (version "v1.1.15"))
+    (require (module-path "launchpad.net/~user/project/branch")
+             (version "v1.1.16"))
+    (require (module-path "launchpad.net/~user/project/branch/sub/directory")
+             (version "v1.1.17"))
+    (require (module-path "hub.jazz.net/git/user/project")
+             (version "v1.1.18"))
+    (require (module-path "hub.jazz.net/git/user/project/sub/directory")
+             (version "v1.1.19"))
+    (require (module-path "k8s.io/kubernetes/subproject")
+             (version "v1.1.101"))
+    (require (module-path "one.example.com/abitrary/repo")
+             (version "v1.1.111"))
+    (require (module-path "two.example.com/abitrary/repo")
+             (version "v0.0.2"))
+    (require (module-path "quoted.example.com/abitrary/repo")
+             (version "v0.0.2"))
+    (replace (original (module-path "two.example.com/abitrary/repo"))
+      (with (module-path "github.com/corp/arbitrary-repo")
+            (version "v0.0.2")))
+    (replace (original (module-path "golang.org/x/sys"))
+      (with (module-path "golang.org/x/sys")
+            (version "v0.0.0-20190813064441-fde4db37ae7a"))
+      (comment "pinned to release-branch.go1.13"))
+    (replace (original (module-path "golang.org/x/tools"))
+      (with (module-path "golang.org/x/tools")
+            (version "v0.0.0-20190821162956-65e3620a7ae7"))
+      (comment "pinned to release-branch.go1.13")))
+  (parse-go.mod fixture-go-mod-complete))
+
 ;;; End-to-end tests for (guix import go)
 (define (mock-http-fetch testcase)
   (lambda (url . rest)