diff --git a/src/nzg_spaces.c b/src/nzg_spaces.c
index 1d42190..3d4637e 100644
--- a/src/nzg_spaces.c
+++ b/src/nzg_spaces.c
@@ -52,7 +52,7 @@ msgSpace * msgSpaceCreate(
   mSAddr = mmap( 0, sizeof( *mSAddr ),
             PROT_READ | PROT_WRITE,
             MAP_SHARED, mSFd, 0 );
-    if( mSAddr == NULL ) {
+    if( mSAddr == MAP_FAILED ) {
         fprintf( stderr, "mmap failed: %s\n",
             strerror( errno ) );
         return NULL;