diff --git a/cmake/attrib.cmake b/cmake/attrib.cmake
index 6ce3f2a7..5600ce6b 100644
--- a/cmake/attrib.cmake
+++ b/cmake/attrib.cmake
@@ -1,3 +1,13 @@
 # tests for compiler properties
 
-CHECK_C_SOURCE_COMPILES("int foo(int) __attribute__ ((ifunc(\"foo_i\"))); int f1(int i) { return i; } void (*foo_i()) { return f1; } int main(void) { return 0; }" HAS_C_ATTR_IFUNC)
+# set -Werror so we can't ignore unused attribute warnings
+set (CMAKE_REQUIRED_FLAGS "-Werror")
+
+CHECK_C_SOURCE_COMPILES("
+    int foo(int) __attribute__ ((ifunc(\"foo_i\")));
+    int f1(int i) { return i; }
+    void (*foo_i()) { return f1; }
+    int main(void) { return 0; }
+    " HAS_C_ATTR_IFUNC)
+
+unset(CMAKE_REQUIRED_FLAGS)