diff --git a/tests/testsuite.h b/tests/testsuite.h
index 7e8e0599..e4c8298d 100644
--- a/tests/testsuite.h
+++ b/tests/testsuite.h
@@ -7,7 +7,7 @@
 /* In C++ pre C++11 it is standard practice to use 0 for the null
    pointer.  But GCC -std=c++98 with -Wzero-as-null-pointer-constant
    warns about this.  Warning introduced in GCC 4.7. */
-#if !defined __cplusplus || __cplusplus < 201103L
+#if defined __cplusplus && __cplusplus < 201103L
 # if defined __GNUC__ && ! defined __clang__ && 407 <= __GNUC__ * 100 + __GNUC_MINOR__
 #  pragma GCC diagnostic ignored "-Wzero-as-null-pointer-constant"
 # endif