diff --git a/src/muz/base/dl_util.cpp b/src/muz/base/dl_util.cpp
index 2dbf844a8..e8a1c5139 100644
--- a/src/muz/base/dl_util.cpp
+++ b/src/muz/base/dl_util.cpp
@@ -622,10 +622,10 @@ namespace datalog {
     }
 
     bool string_to_uint64(const char * s, uint64_t & res) {
-#if 1
+#if _WINDOWS
         int converted = sscanf_s(s, "%I64u", &res);
 #else
-        int converted = sscanf(s, "%llu", &res);
+        int converted = sscanf(s, "%I64u", &res);
 #endif
         if(converted==0) {
             return false;