diff --git a/compiler/optimizing/ssa_builder.cc b/compiler/optimizing/ssa_builder.cc
index 50e3254..33084df 100644
--- a/compiler/optimizing/ssa_builder.cc
+++ b/compiler/optimizing/ssa_builder.cc
@@ -19,6 +19,18 @@
 
 namespace art {
 
+static Primitive::Type MergeTypes(Primitive::Type existing, Primitive::Type new_type) {
+  // We trust the verifier has already done the necessary checking.
+  switch (existing) {
+    case Primitive::kPrimFloat:
+    case Primitive::kPrimDouble:
+    case Primitive::kPrimNot:
+      return existing;
+    default:
+      return new_type;
+  }
+}
+
 void SsaBuilder::BuildSsa() {
   // 1) Visit in reverse post order. We need to have all predecessors of a block visited
   // (with the exception of loops) in order to create the right environment for that
@@ -32,11 +44,16 @@
     HBasicBlock* block = loop_headers_.Get(i);
     for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) {
       HPhi* phi = it.Current()->AsPhi();
+      Primitive::Type type = Primitive::kPrimVoid;
       for (size_t pred = 0; pred < block->GetPredecessors().Size(); pred++) {
-        phi->AddInput(ValueOfLocal(block->GetPredecessors().Get(pred), phi->GetRegNumber()));
+        HInstruction* input = ValueOfLocal(block->GetPredecessors().Get(pred), phi->GetRegNumber());
+        phi->AddInput(input);
+        type = MergeTypes(type, input->GetType());
       }
+      phi->SetType(type);
     }
   }
+  // TODO: Now that the type of loop phis is set, we need a type propagation phase.
 
   // 3) Clear locals.
   // TODO: Move this to a dead code eliminator phase.
@@ -65,7 +82,6 @@
     for (size_t local = 0; local < current_locals_->Size(); local++) {
       HInstruction* incoming = ValueOfLocal(block->GetLoopInformation()->GetPreHeader(), local);
       if (incoming != nullptr) {
-        // TODO: Compute union type.
         HPhi* phi = new (GetGraph()->GetArena()) HPhi(
             GetGraph()->GetArena(), local, 0, Primitive::kPrimVoid);
         block->AddPhi(phi);
@@ -88,12 +104,18 @@
         }
       }
       if (is_different) {
-        // TODO: Compute union type.
         HPhi* phi = new (GetGraph()->GetArena()) HPhi(
             GetGraph()->GetArena(), local, block->GetPredecessors().Size(), Primitive::kPrimVoid);
+        Primitive::Type type = Primitive::kPrimVoid;
         for (size_t i = 0; i < block->GetPredecessors().Size(); i++) {
-          phi->SetRawInputAt(i, ValueOfLocal(block->GetPredecessors().Get(i), local));
+          HInstruction* value = ValueOfLocal(block->GetPredecessors().Get(i), local);
+          // We need to merge the incoming types, as the Dex format does not
+          // guarantee the inputs have the same type. In particular the 0 constant is
+          // used for all types, but the graph builder treats it as an int.
+          type = MergeTypes(type, value->GetType());
+          phi->SetRawInputAt(i, value);
         }
+        phi->SetType(type);
         block->AddPhi(phi);
         value = phi;
       }