diff --git a/algorithm.c b/algorithm.c
index f2c90d5b..b41bbc2b 100644
--- a/algorithm.c
+++ b/algorithm.c
@@ -124,7 +124,7 @@ static void append_scrypt_compiler_options(struct _build_kernel_data *data, stru
 static void append_ethash_compiler_options(struct _build_kernel_data *data, struct cgpu_info *cgpu, struct _algorithm_t *algorithm)
 {
 #ifdef WIN32
-  strcat(data->compiler_options, "-DWINDOWS");
+  strcat(data->compiler_options, " -DWINDOWS");
 #endif
 }