diff --git a/gnu/local.mk b/gnu/local.mk
index 6888396095..b47cf01e0c 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -1622,6 +1622,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/owncloud-disable-updatecheck.patch	\
   %D%/packages/patches/p7zip-CVE-2016-9296.patch		\
   %D%/packages/patches/p7zip-CVE-2017-17969.patch		\
+  %D%/packages/patches/p7zip-fix-build-with-gcc-11.patch	\
   %D%/packages/patches/p7zip-remove-unused-code.patch		\
   %D%/packages/patches/pam-krb5-CVE-2020-10595.patch		\
   %D%/packages/patches/pango-skip-libthai-test.patch		\
diff --git a/gnu/packages/compression.scm b/gnu/packages/compression.scm
index 0e7c300fc9..0365b37fa4 100644
--- a/gnu/packages/compression.scm
+++ b/gnu/packages/compression.scm
@@ -1339,6 +1339,7 @@ for most inputs, but the resulting compressed files are anywhere from 20% to
                      "switch(static_cast<HRESULT>(errorCode)) {"))))
               (patches (search-patches "p7zip-CVE-2016-9296.patch"
                                        "p7zip-CVE-2017-17969.patch"
+                                       "p7zip-fix-build-with-gcc-11.patch"
                                        "p7zip-remove-unused-code.patch"))))
     (build-system gnu-build-system)
     (arguments
diff --git a/gnu/packages/patches/p7zip-fix-build-with-gcc-11.patch b/gnu/packages/patches/p7zip-fix-build-with-gcc-11.patch
new file mode 100644
index 0000000000..20a40488d8
--- /dev/null
+++ b/gnu/packages/patches/p7zip-fix-build-with-gcc-11.patch
@@ -0,0 +1,49 @@
+Building p7zip with GCC 11 or newer normally fails with error messages like
+
+  ../../../../CPP/7zip/Archive/Wim/WimHandler.cpp:308:11: error: use of an
+  operand of type ‘bool’ in ‘operator++’ is forbidden in C++17
+    308 |           numMethods++;
+        |           ^~~~~~~~~~
+
+This patch causes GCC to interpret the code using the GNU dialect of the C++14
+standard, as GCC 10 did by default, and reduces these errors to warnings.
+
+diff --git a/makefile.linux_amd64_asm b/makefile.linux_amd64_asm
+index 075c6a8..b7d73ee 100644
+--- a/makefile.linux_amd64_asm
++++ b/makefile.linux_amd64_asm
+@@ -11,6 +11,8 @@ ALLFLAGS=-m64 ${OPTFLAGS} -pipe \
+ 	-D_7ZIP_ASM \
+ 	$(LOCAL_FLAGS)
+ 
++ALLFLAGS_CPP=-std=gnu++14
++
+ CXX=g++
+ CC=gcc
+ CC_SHARED=-fPIC
+diff --git a/makefile.linux_any_cpu_gcc_4.X b/makefile.linux_any_cpu_gcc_4.X
+index be093b5..c0f3120 100644
+--- a/makefile.linux_any_cpu_gcc_4.X
++++ b/makefile.linux_any_cpu_gcc_4.X
+@@ -10,7 +10,7 @@ ALLFLAGS=${OPTFLAGS} -pipe \
+ 	-D_7ZIP_LARGE_PAGES \
+ 	$(LOCAL_FLAGS)
+ 
+-ALLFLAGS_CPP=-DENV_HAVE_GCCVISIBILITYPATCH -fvisibility=hidden -fvisibility-inlines-hidden
++ALLFLAGS_CPP=-DENV_HAVE_GCCVISIBILITYPATCH -std=gnu++14 -fvisibility=hidden -fvisibility-inlines-hidden
+ 
+ CXX=g++
+ CC=gcc
+diff --git a/makefile.linux_x86_asm_gcc_4.X b/makefile.linux_x86_asm_gcc_4.X
+index 1ac339b..6e736d9 100644
+--- a/makefile.linux_x86_asm_gcc_4.X
++++ b/makefile.linux_x86_asm_gcc_4.X
+@@ -12,7 +12,7 @@ ALLFLAGS=${OPTFLAGS} -pipe -m32 \
+ 	-D_7ZIP_ASM \
+ 	$(LOCAL_FLAGS)
+ 
+-ALLFLAGS_CPP=-DENV_HAVE_GCCVISIBILITYPATCH -fvisibility=hidden -fvisibility-inlines-hidden
++ALLFLAGS_CPP=-DENV_HAVE_GCCVISIBILITYPATCH -std=gnu++14 -fvisibility=hidden -fvisibility-inlines-hidden
+ 
+ CXX=g++
+ CC=gcc