diff --git a/configure b/configure
index 1d2522483a8..0d3f634abec 100755
--- a/configure
+++ b/configure
@@ -16986,6 +16986,14 @@ rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
 fi
 
 
+# These flags are supported in all C11-capable GCC/Clang versions,
+# so no capability test is needed.  Added here to avoid affecting configure probes,
+# particularly PGAC_PRINTF_ARCHETYPE which uses -Werror and would fail to detect
+# gnu_printf if -Wstrict-prototypes is active.
+if test "$GCC" = yes -a "$ICC" = no; then
+  CFLAGS="$CFLAGS -Wstrict-prototypes -Wold-style-definition"
+fi
+
 # --------------------
 # Run tests below here
 # --------------------
diff --git a/configure.ac b/configure.ac
index 70ddcaabc44..f8327a7020a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2027,6 +2027,14 @@ related to locating shared libraries.  Check the file 'config.log'
 for the exact reason.]])],
 [AC_MSG_RESULT([cross-compiling])])
 
+# These flags are supported in all C11-capable GCC/Clang versions,
+# so no capability test is needed.  Added here to avoid affecting configure probes,
+# particularly PGAC_PRINTF_ARCHETYPE which uses -Werror and would fail to detect
+# gnu_printf if -Wstrict-prototypes is active.
+if test "$GCC" = yes -a "$ICC" = no; then
+  CFLAGS="$CFLAGS -Wstrict-prototypes -Wold-style-definition"
+fi
+
 # --------------------
 # Run tests below here
 # --------------------
diff --git a/meson.build b/meson.build
index c6e7cae5055..0a181909fab 100644
--- a/meson.build
+++ b/meson.build
@@ -2253,6 +2253,8 @@ if cc.has_argument('-Wmissing-variable-declarations')
   cflags_no_missing_var_decls += '-Wno-missing-variable-declarations'
 endif
 
+# These are C-only flags, supported in all C11-capable GCC/Clang versions.
+cflags_warn += cc.get_supported_arguments(['-Wstrict-prototypes', '-Wold-style-definition'])
 
 # The following tests want to suppress various unhelpful warnings by adding
 # -Wno-foo switches.  But gcc won't complain about unrecognized -Wno-foo
diff --git a/src/bin/psql/input.h b/src/bin/psql/input.h
index 09961c84101..2a47166347e 100644
--- a/src/bin/psql/input.h
+++ b/src/bin/psql/input.h
@@ -17,6 +17,15 @@
 #ifdef HAVE_LIBREADLINE
 #define USE_READLINE 1
 
+/*
+ * Readline headers trigger a lot of warnings with our preferred compiler flags
+ * (at least -Wstrict-prototypes is known to be problematic). The system_header
+ * pragma hides warnings from within the rest of this file, if supported.
+ */
+#ifdef HAVE_PRAGMA_GCC_SYSTEM_HEADER
+#pragma GCC system_header
+#endif
+
 #if defined(HAVE_READLINE_READLINE_H)
 #include <readline/readline.h>
 #if defined(HAVE_READLINE_HISTORY_H)