1 files changed, 9 insertions, 0 deletions
diff --git a/generic/tkTextDisp.c b/generic/tkTextDisp.c
index c3ea9e0..b9790db 100644
--- a/generic/tkTextDisp.c
+++ b/generic/tkTextDisp.c
@@ -6972,6 +6972,15 @@ TkTextDLineInfo(
      */
 
     dlPtr = FindDLine(textPtr, dInfoPtr->dLinePtr, indexPtr);
+
+    /* 
+     * Two cases shall be trapped here because the logic later really
+     * needs dlPtr to be the display line containing indexPtr:
+     *   1. if no display line contains the desired index (NULL dlPtr)
+     *   2. if indexPtr is before the first display line, in which case
+     *      dlPtr currently points to the first display line
+     */
+
     if ((dlPtr == NULL) || (TkTextIndexCmp(&dlPtr->index, indexPtr) > 0)) {
 	return -1;
     }