diff --git a/ac/gcc_version.m4 b/ac/gcc_version.m4
index fc1e88146..abfdcd564 100644
--- a/ac/gcc_version.m4
+++ b/ac/gcc_version.m4
@@ -1,4 +1,4 @@
 AC_CACHE_CHECK(
   [gcc version],
   [ac_cv_gcc_version],
-  [ac_cv_gcc_version=`$ac_cv_prog_CXX -dumpversion | sed -e 's/[[^0-9\.]]//g'`])
+  [ac_cv_gcc_version=`$CXX -dumpversion | sed -e 's/[[^0-9\.]].*//g'`])