diff --git a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
--- a/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionSpecialization.cpp
@@ -190,7 +190,10 @@
   if (I.getCondition() != LastVisited->first)
     return 0;
 
-  auto *C = cast<ConstantInt>(LastVisited->second);
+  auto *C = dyn_cast<ConstantInt>(LastVisited->second);
+  if (!C)
+    return 0;
+
   BasicBlock *Succ = I.findCaseValue(C)->getCaseSuccessor();
   // Initialize the worklist with the dead basic blocks. These are the
   // destination labels which are different from the one corresponding
diff --git a/llvm/test/Transforms/FunctionSpecialization/function-specialization-constant-expression6.ll b/llvm/test/Transforms/FunctionSpecialization/function-specialization-constant-expression6.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/FunctionSpecialization/function-specialization-constant-expression6.ll
@@ -0,0 +1,22 @@
+; RUN: opt -passes="ipsccp<func-spec>" -force-specialization -S < %s
+; Check that we don't crash when SwitchInst Constant is not ConstantInt.
+
+@S = external constant [1 x i8]
+
+define i1 @foo() {
+entry:
+  %tmp = call i32 @bar(ptr @S)
+  ret i1 0
+}
+
+define i32 @bar(ptr %arg) {
+entry:
+  %magicptr = ptrtoint ptr %arg to i64
+  switch i64 %magicptr, label %bb2 [
+    i64 0, label %bb1
+  ]
+bb1:
+  ret i32 0
+bb2:
+  ret i32 1
+}