Index: llvm/lib/IR/Globals.cpp
===================================================================
--- llvm/lib/IR/Globals.cpp
+++ llvm/lib/IR/Globals.cpp
@@ -359,6 +359,21 @@
   getParent()->getGlobalList().erase(getIterator());
 }
 
+static void assertThatAllGlobalsAreIn(Constant *Value, Module *Correct) {
+  if(ConstantStruct *V = dyn_cast<ConstantStruct>(Value)) {
+    int n = V->getNumOperands();
+    while(n)
+      assertThatAllGlobalsAreIn(V->getOperand(--n), Correct);
+  } else if(ConstantArray *V = dyn_cast<ConstantArray>(Value)) {
+    int n = V->getType()->getNumElements();
+    while(n)
+      assertThatAllGlobalsAreIn(V->getAggregateElement(--n), Correct);
+  } else if(GlobalValue *V = dyn_cast<GlobalValue>(Value)) {
+    assert((!V->getParent() || V->getParent() == Correct) &&
+           "A Constant and its initializer cannot be in different modules");
+  }
+}
+
 void GlobalVariable::setInitializer(Constant *InitVal) {
   if (!InitVal) {
     if (hasInitializer()) {
@@ -377,6 +392,7 @@
     if (!hasInitializer())
       setGlobalVariableNumOperands(1);
     Op<0>().set(InitVal);
+    assertThatAllGlobalsAreIn(InitVal, getParent());
   }
 }