--- a/js/src/jit/LoopUnroller.cpp
+++ b/js/src/jit/LoopUnroller.cpp
@@ -16,17 +16,20 @@ using mozilla::ArrayLength;
 namespace {
 
 struct LoopUnroller
 {
     typedef HashMap<MDefinition*, MDefinition*,
                     PointerHasher<MDefinition*, 2>, SystemAllocPolicy> DefinitionMap;
 
     explicit LoopUnroller(MIRGraph& graph)
-      : graph(graph), alloc(graph.alloc())
+      : graph(graph), alloc(graph.alloc()),
+        header(nullptr), backedge(nullptr),
+        unrolledHeader(nullptr), unrolledBackedge(nullptr),
+        oldPreheader(nullptr), newPreheader(nullptr)
     {}
 
     MIRGraph& graph;
     TempAllocator& alloc;
 
     // Header and body of the original loop.
     MBasicBlock* header;
     MBasicBlock* backedge;