diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
index c858f84..c420676 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -147,6 +147,7 @@
   - "modules"
     This declares the symbol to be used as the MODULES symbol, which
     enables the third modular state for all config symbols.
+    At most one symbol may have the "modules" option set.
 
   - "env"=<value>
     This imports the environment variable into Kconfig. It behaves like
diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index 3a9c674..c1d5320 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -199,6 +199,12 @@
 {
 	switch (token) {
 	case T_OPT_MODULES:
+		if (modules_sym)
+			zconf_error("symbol '%s' redefines option 'modules'"
+				    " already defined by symbol '%s'",
+				    current_entry->sym->name,
+				    modules_sym->name
+				    );
 		modules_sym = current_entry->sym;
 		break;
 	case T_OPT_DEFCONFIG_LIST: