1 files changed, 1 insertions, 1 deletions
diff --git a/generic/tclIO.c b/generic/tclIO.c
index b480377..552cab5 100644
--- a/generic/tclIO.c
+++ b/generic/tclIO.c
@@ -6259,7 +6259,7 @@ ReadChars(
     int dstLimit = TCL_UTF_MAX - 1 + toRead * factor / UTF_EXPANSION_FACTOR;
 
     (void) Tcl_GetStringFromObj(objPtr, &numBytes);
-    Tcl_AppendToObj(objPtr, NULL, dstLimit);
+    Tcl_SetObjLength(objPtr, numBytes + dstLimit);
     if (toRead == srcLen) {
 	Tcl_Size size;