diff --git a/src/include/c.h b/src/include/c.h
index 4f16e589b3..863a16c6a6 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -144,6 +144,17 @@
 #define pg_attribute_no_sanitize_alignment()
 #endif
 
+/*
+ * pg_attribute_nonnull means the compiler should warn if the function is
+ * called with the listed arguments set to NULL.  If no arguments are
+ * listed, the compiler should warn if any pointer arguments are set to NULL.
+ */
+#if __has_attribute (nonnull)
+#define pg_attribute_nonnull(...) __attribute__((nonnull(__VA_ARGS__)))
+#else
+#define pg_attribute_nonnull(...)
+#endif
+
 /*
  * Append PG_USED_FOR_ASSERTS_ONLY to definitions of variables that are only
  * used in assert-enabled builds, to avoid compiler warnings about unused
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index d5976ecbfb..4d0920c42e 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -307,7 +307,7 @@ extern void DefineCustomBoolVariable(const char *name,
 									 int flags,
 									 GucBoolCheckHook check_hook,
 									 GucBoolAssignHook assign_hook,
-									 GucShowHook show_hook);
+									 GucShowHook show_hook) pg_attribute_nonnull(1, 4);
 
 extern void DefineCustomIntVariable(const char *name,
 									const char *short_desc,
@@ -320,7 +320,7 @@ extern void DefineCustomIntVariable(const char *name,
 									int flags,
 									GucIntCheckHook check_hook,
 									GucIntAssignHook assign_hook,
-									GucShowHook show_hook);
+									GucShowHook show_hook) pg_attribute_nonnull(1, 4);
 
 extern void DefineCustomRealVariable(const char *name,
 									 const char *short_desc,
@@ -333,7 +333,7 @@ extern void DefineCustomRealVariable(const char *name,
 									 int flags,
 									 GucRealCheckHook check_hook,
 									 GucRealAssignHook assign_hook,
-									 GucShowHook show_hook);
+									 GucShowHook show_hook) pg_attribute_nonnull(1, 4);
 
 extern void DefineCustomStringVariable(const char *name,
 									   const char *short_desc,
@@ -344,7 +344,7 @@ extern void DefineCustomStringVariable(const char *name,
 									   int flags,
 									   GucStringCheckHook check_hook,
 									   GucStringAssignHook assign_hook,
-									   GucShowHook show_hook);
+									   GucShowHook show_hook) pg_attribute_nonnull(1, 4);
 
 extern void DefineCustomEnumVariable(const char *name,
 									 const char *short_desc,
@@ -356,7 +356,7 @@ extern void DefineCustomEnumVariable(const char *name,
 									 int flags,
 									 GucEnumCheckHook check_hook,
 									 GucEnumAssignHook assign_hook,
-									 GucShowHook show_hook);
+									 GucShowHook show_hook) pg_attribute_nonnull(1, 4);
 
 extern void MarkGUCPrefixReserved(const char *className);