diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 0913be72c6..3719bbc7ca 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -56,6 +56,7 @@ else()
         -Werror=implicit-fallthrough
         -Werror=reorder
         -Wextra
+        -Wmissing-declarations
         -Wno-attributes
         -Wno-unused-parameter
     )