diff --git a/js/src/jstracer.cpp b/js/src/jstracer.cpp
index 6542c196579..9d65ed01418 100644
--- a/js/src/jstracer.cpp
+++ b/js/src/jstracer.cpp
@@ -1308,6 +1308,19 @@ TypeMap::matches(TypeMap& other) const
     return !memcmp(data(), other.data(), length());
 }
 
+/* Use the provided storage area to create a new type map that contains the partial type map
+   with the rest of it filled up from the complete type map. */
+static void
+mergeTypeMaps(uint8** partial, unsigned* plength, uint8* complete, unsigned clength, uint8* mem)
+{
+    unsigned l = *plength;
+    JS_ASSERT(l < clength);
+    memcpy(mem, *partial, l * sizeof(uint8));
+    memcpy(mem + l, complete + l, (clength - l) * sizeof(uint8));
+    *partial = mem;
+    *plength = clength;
+}
+
 /* Specializes a tree to any missing globals, including any dependent trees. */
 static JS_REQUIRES_STACK void
 specializeTreesToMissingGlobals(JSContext* cx, TreeInfo* root)
@@ -2077,16 +2090,29 @@ JS_REQUIRES_STACK void
 TraceRecorder::import(TreeInfo* treeInfo, LIns* sp, unsigned stackSlots, unsigned ngslots,
                       unsigned callDepth, uint8* typeMap)
 {
+    /* If we get a partial list that doesn't have all the types (i.e. recording from a side
+       exit that was recorded but we added more global slots later), merge the missing types
+       from the entry type map. This is safe because at the loop edge we verify that we
+       have compatible types for all globals (entry type and loop edge type match). While
+       a different trace of the tree might have had a guard with a different type map for
+       these slots we just filled in here (the guard we continue from didn't know about them),
+       since we didn't take that particular guard the only way we could have ended up here
+       is if that other trace had at its end a compatible type distribution with the entry
+       map. Since thats exactly what we used to fill in the types our current side exit
+       didn't provide, this is always safe to do. */
+
+    uint8* globalTypeMap = typeMap + stackSlots;
+    unsigned length = treeInfo->nGlobalTypes();
+
     /*
-     * If we get a partial list that doesn't have all the types, capture the missing types
-     * from the current environment.
+     * This is potentially the typemap of the side exit and thus shorter than the tree's
+     * global type map.
      */
-    TypeMap fullTypeMap(typeMap, stackSlots + ngslots);
-    if (ngslots < treeInfo->globalSlots->length()) {
-        fullTypeMap.captureMissingGlobalTypes(cx, *treeInfo->globalSlots, stackSlots);
-        ngslots = treeInfo->globalSlots->length();
+    if (ngslots < length) {
+        mergeTypeMaps(&globalTypeMap/*out param*/, &ngslots/*out param*/,
+                      treeInfo->globalTypeMap(), length,
+                      (uint8*)alloca(sizeof(uint8) * length));
     }
-    uint8* globalTypeMap = fullTypeMap.data() + stackSlots;
     JS_ASSERT(ngslots == treeInfo->nGlobalTypes());
 
     /*
diff --git a/js/src/jstracer.h b/js/src/jstracer.h
index 9f709e6fd2a..3ae2587fd06 100644
--- a/js/src/jstracer.h
+++ b/js/src/jstracer.h
@@ -76,13 +76,6 @@ public:
         this->_data = (T*)malloc(max * sizeof(T));
     }
 
-    Queue(T* data, unsigned length) {
-        this->_max =
-        this->_len = length;
-        this->_data = (T*)malloc(length * sizeof(T));
-        memcpy(this->_data, data, length);
-    }
-
     ~Queue() {
         free(_data);
     }
@@ -196,12 +189,6 @@ typedef Queue<uint16> SlotList;
 
 class TypeMap : public Queue<uint8> {
 public:
-    TypeMap() : Queue<uint8>() {
-    }
-
-    TypeMap(uint8* partial, unsigned length) : Queue<uint8>(partial, length) {
-    }
-
     JS_REQUIRES_STACK void captureTypes(JSContext* cx, SlotList& slots, unsigned callDepth);
     JS_REQUIRES_STACK void captureMissingGlobalTypes(JSContext* cx,
                                                      SlotList& slots,