diff --git a/runtime/vm/cha.cc b/runtime/vm/cha.cc
index b960a147539..b937357800c 100644
--- a/runtime/vm/cha.cc
+++ b/runtime/vm/cha.cc
@@ -71,6 +71,8 @@ bool CHA::HasSubclasses(intptr_t cid) {
 
 
 bool CHA::IsImplemented(const Class& cls) {
+  // Signature classes have different type checking rules.
+  ASSERT(!cls.IsSignatureClass());
   // Can't track dependencies for classes on the VM heap since those are
   // read-only.
   // TODO(fschneider): Enable tracking of CHA dependent code for VM heap
diff --git a/runtime/vm/flow_graph_type_propagator.cc b/runtime/vm/flow_graph_type_propagator.cc
index ed42cb71810..d7e639670b0 100644
--- a/runtime/vm/flow_graph_type_propagator.cc
+++ b/runtime/vm/flow_graph_type_propagator.cc
@@ -511,7 +511,10 @@ intptr_t CompileType::ToNullableCid() {
       if (FLAG_use_cha) {
         const Class& type_class = Class::Handle(type_->type_class());
         CHA* cha = Isolate::Current()->cha();
-        if (!cha->IsImplemented(type_class) &&
+        // Don't infer a cid from an abstract type for signature classes since
+        // there can be multiple compatible classes with different cids.
+        if (!type_class.IsSignatureClass() &&
+            !cha->IsImplemented(type_class) &&
             !cha->HasSubclasses(type_class.id())) {
           cid_ = type_class.id();
         } else {