diff --git a/fxjs/xfa/cfxjse_formcalc_context.cpp b/fxjs/xfa/cfxjse_formcalc_context.cpp
index 790ec94..695cc25 100644
--- a/fxjs/xfa/cfxjse_formcalc_context.cpp
+++ b/fxjs/xfa/cfxjse_formcalc_context.cpp
@@ -630,7 +630,7 @@
     if (FXSYS_atoi(szBuffer) > 60) {
       return false;
     }
-    if (pData[2] == ':') {
+    if (iIndex + 2 < iZone && pData[iIndex + 2] == ':') {
       if (iPos == 0) {
         iHour = FXSYS_atoi(szBuffer);
         ++iPos;
@@ -701,7 +701,7 @@
     if (FXSYS_atoi(szBuffer) > 60) {
       return false;
     }
-    if (pData[2] == ':') {
+    if (iIndex + 2 < pData.size() && pData[iIndex + 2] == ':') {
       if (iPos == 0) {
         iZoneHour = FXSYS_atoi(szBuffer);
       } else if (iPos == 1) {