diff --git a/lib/Analysis/DataStructure/CompleteBottomUp.cpp b/lib/Analysis/DataStructure/CompleteBottomUp.cpp
index 95c9d3c..87b96b2 100644
--- a/lib/Analysis/DataStructure/CompleteBottomUp.cpp
+++ b/lib/Analysis/DataStructure/CompleteBottomUp.cpp
@@ -71,7 +71,8 @@
   unsigned NextID = 1;
 
   if (Function *Main = M.getMainFunction()) {
-    calculateSCCGraphs(getOrCreateGraph(*Main), Stack, NextID, ValMap);
+    if (!Main->isExternal())
+      calculateSCCGraphs(getOrCreateGraph(*Main), Stack, NextID, ValMap);
   } else {
     std::cerr << "CBU-DSA: No 'main' function found!\n";
   }