1 files changed, 6 insertions, 0 deletions
diff --git a/generic/tclCmdMZ.c b/generic/tclCmdMZ.c
index 11a6661..02eabe0 100644
--- a/generic/tclCmdMZ.c
+++ b/generic/tclCmdMZ.c
@@ -1338,6 +1338,9 @@ StringFirstCmd(
 	    return TCL_ERROR;
 	}
     }
+    if (start < -1) {
+	start = -1;
+    }
     Tcl_SetObjResult(interp, TclNewWideIntObjFromSize(TclStringFirst(objv[1],
 	    objv[2], start)));
     return TCL_OK;
@@ -1383,6 +1386,9 @@ StringLastCmd(
 	    return TCL_ERROR;
 	}
     }
+    if (last < -1) {
+	last = -1;
+    }
     Tcl_SetObjResult(interp, TclNewWideIntObjFromSize(TclStringLast(objv[1],
 	    objv[2], last)));
     return TCL_OK;