diff --git a/libtransmission/utils.c b/libtransmission/utils.c
index c09295791..4a37b6ef1 100644
--- a/libtransmission/utils.c
+++ b/libtransmission/utils.c
@@ -519,13 +519,17 @@ tr_mkdtemp( char * template )
 #endif
 }
 
-int
-tr_mkdir( const char * path,
-          int permissions
-#ifdef WIN32
-                       UNUSED
-#endif
-        )
+/**
+ * @brief Portability wrapper for mkdir()
+ *
+ * A portability wrapper around mkdir().
+ * On WIN32, the `permissions' argument is unused.
+ *
+ * @return zero on success, or -1 if an error occurred
+ * (in which case errno is set appropriately).
+ */
+static int
+tr_mkdir( const char * path, int permissions UNUSED)
 {
 #ifdef WIN32
     if( path && isalpha( path[0] ) && path[1] == ':' && !path[2] )
diff --git a/libtransmission/utils.h b/libtransmission/utils.h
index 8d8df7618..c5a2437f2 100644
--- a/libtransmission/utils.h
+++ b/libtransmission/utils.h
@@ -203,17 +203,6 @@ char* tr_basename( const char * path ) TR_GNUC_MALLOC;
 /** @brief Portability wrapper for dirname() that uses the system implementation if available */
 char* tr_dirname( const char * path ) TR_GNUC_MALLOC;
 
-/**
- * @brief Portability wrapper for mkdir()
- *
- * A portability wrapper around mkdir().
- * On WIN32, the `permissions' argument is unused.
- *
- * @return zero on success, or -1 if an error occurred
- * (in which case errno is set appropriately).
- */
-int tr_mkdir( const char * path, int permissions ) TR_GNUC_NONNULL(1);
-
 /**
  * Like mkdir, but makes parent directories as needed.
  *