diff --git generic/tclIO.c generic/tclIO.c
index 7e83e890b1..e7656eea1f 100644
--- generic/tclIO.c
+++ generic/tclIO.c
@@ -5208,7 +5208,7 @@ FreeBinaryEncoding(
 }
 
 static Tcl_Encoding
-GetBinaryEncoding()
+GetBinaryEncoding(void)
 {
     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
 
