diff --git a/src/mcdlutil.cpp b/src/mcdlutil.cpp
index 9dbd1cdd4..82823c056 100644
--- a/src/mcdlutil.cpp
+++ b/src/mcdlutil.cpp
@@ -628,7 +628,7 @@ namespace OpenBabel {
 
   int TSingleBond::getValence() {
     int result=0;
-    if (this->tb <=NBONDTYPES) result=bondValence[this->tb-1];
+    if (this->tb >= 1 && this->tb <= NBONDTYPES) result=bondValence[this->tb-1];
     return result;
   };