diff --git a/utils/InMemoryFile.cc b/utils/InMemoryFile.cc
index b7865fe..702a105 100644
--- a/utils/InMemoryFile.cc
+++ b/utils/InMemoryFile.cc
@@ -58,7 +58,7 @@
 
 FILE* InMemoryFile::open(const char* mode)
 {
-#if HAVE_IN_MEMORY_FILE_FOPENCOOKIE
+#ifdef HAVE_IN_MEMORY_FILE_FOPENCOOKIE
     if (fptr != nullptr) {
         fprintf(stderr, "InMemoryFile: BUG: Why is this opened more than once?");
         return nullptr; // maybe there's some legit reason for it, whoever comes up with one can remove this line