diff --git a/lib/Transforms/IPO/PruneEH.cpp b/lib/Transforms/IPO/PruneEH.cpp
index ceb9e3e54e8..d2f3a8437cf 100644
--- a/lib/Transforms/IPO/PruneEH.cpp
+++ b/lib/Transforms/IPO/PruneEH.cpp
@@ -64,6 +64,8 @@ bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
 
   // Next, check to see if any callees might throw or if there are any external
   // functions in this SCC: if so, we cannot prune any functions in this SCC.
+  // Definitions that are weak and not declared non-throwing might be 
+  // overridden at linktime with something that throws, so assume that.
   // If this SCC includes the unwind instruction, we KNOW it throws, so
   // obviously the SCC might throw.
   //
@@ -71,7 +73,7 @@ bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
   for (unsigned i = 0, e = SCC.size();
        (!SCCMightUnwind || !SCCMightReturn) && i != e; ++i) {
     Function *F = SCC[i]->getFunction();
-    if (F == 0) {
+    if (F == 0 || (F->hasWeakLinkage() && !F->doesNotThrow())) {
       SCCMightUnwind = true;
       SCCMightReturn = true;
     } else if (F->isDeclaration()) {