diff --git a/src/openrct2/util/Util.cpp b/src/openrct2/util/Util.cpp
index 26ba239cd8..ff58a84a42 100644
--- a/src/openrct2/util/Util.cpp
+++ b/src/openrct2/util/Util.cpp
@@ -483,7 +483,7 @@ char* safe_strtrimleft(char* destination, const char* source, size_t size)
     return safe_strcpy(destination, source, size);
 }
 
-#if !(defined(_GNU_SOURCE) || (defined(__DARWIN_C_LEVEL) && __DARWIN_C_LEVEL >= 200809L))
+#if defined(_WIN32)
 char* strcasestr(const char* haystack, const char* needle)
 {
     const char* p1 = haystack;
diff --git a/src/openrct2/util/Util.h b/src/openrct2/util/Util.h
index bf4dc23f41..462e46308a 100644
--- a/src/openrct2/util/Util.h
+++ b/src/openrct2/util/Util.h
@@ -44,7 +44,7 @@ char* safe_strcpy(char* destination, const char* source, size_t num);
 char* safe_strcat(char* destination, const char* source, size_t size);
 char* safe_strcat_path(char* destination, const char* source, size_t size);
 char* safe_strtrimleft(char* destination, const char* source, size_t size);
-#if !(defined(_GNU_SOURCE) || (defined(__DARWIN_C_LEVEL) && __DARWIN_C_LEVEL >= 200809L))
+#if defined(_WIN32)
 char* strcasestr(const char* haystack, const char* needle);
 #endif