diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index 6814e2b446ba..bde31609c982 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -5033,13 +5033,18 @@ BumpStaticLevel(ParseNode *pn, TreeContext *tc)
     return pn->pn_cookie.set(tc->sc->context, level, pn->pn_cookie.slot());
 }
 
-static void
+static bool
 AdjustBlockId(ParseNode *pn, unsigned adjust, TreeContext *tc)
 {
     JS_ASSERT(pn->isArity(PN_LIST) || pn->isArity(PN_FUNC) || pn->isArity(PN_NAME));
+    if (JS_BIT(20) - pn->pn_blockid <= adjust + 1) {
+        JS_ReportErrorNumber(tc->sc->context, js_GetErrorMessage, NULL, JSMSG_NEED_DIET, "program");
+        return false;
+    }
     pn->pn_blockid += adjust;
     if (pn->pn_blockid >= tc->blockidGen)
         tc->blockidGen = pn->pn_blockid + 1;
+    return true;
 }
 
 bool
@@ -5056,8 +5061,10 @@ CompExprTransplanter::transplant(ParseNode *pn)
             if (!transplant(pn2))
                 return false;
         }
-        if (pn->pn_pos >= root->pn_pos)
-            AdjustBlockId(pn, adjust, tc);
+        if (pn->pn_pos >= root->pn_pos) {
+            if (!AdjustBlockId(pn, adjust, tc))
+                return false;
+        }
         break;
 
       case PN_TERNARY:
@@ -5142,7 +5149,8 @@ CompExprTransplanter::transplant(ParseNode *pn)
             if (dn->isPlaceholder() && dn->pn_pos >= root->pn_pos && dn->dn_uses == pn) {
                 if (genexp && !BumpStaticLevel(dn, tc))
                     return false;
-                AdjustBlockId(dn, adjust, tc);
+                if (!AdjustBlockId(dn, adjust, tc))
+                    return false;
             }
 
             RootedAtom atom(parser->context, pn->pn_atom);
@@ -5203,7 +5211,8 @@ CompExprTransplanter::transplant(ParseNode *pn)
                     if (genexp && !visitedImplicitArguments.has(dn)) {
                         if (!BumpStaticLevel(dn, tc))
                             return false;
-                        AdjustBlockId(dn, adjust, tc);
+                        if (!AdjustBlockId(dn, adjust, tc))
+                            return false;
                         if (!visitedImplicitArguments.put(dn))
                             return false;
                     }
@@ -5211,8 +5220,10 @@ CompExprTransplanter::transplant(ParseNode *pn)
             }
         }
 
-        if (pn->pn_pos >= root->pn_pos)
-            AdjustBlockId(pn, adjust, tc);
+        if (pn->pn_pos >= root->pn_pos) {
+            if (!AdjustBlockId(pn, adjust, tc))
+                return false;
+        }
         break;
 
       case PN_NAMESET:
@@ -5292,7 +5303,8 @@ Parser::comprehensionTail(ParseNode *kid, unsigned blockid, bool isGenexp,
     if (!transplanter.init())
         return NULL;
 
-    transplanter.transplant(kid);
+    if (!transplanter.transplant(kid))
+        return false;
 
     JS_ASSERT(tc->blockChain && tc->blockChain == pn->pn_objbox->object);
     data.initLet(HoistVars, *tc->blockChain, JSMSG_ARRAY_INIT_TOO_BIG);
diff --git a/js/src/frontend/TreeContext.cpp b/js/src/frontend/TreeContext.cpp
index b3b301fe1ff0..26a190f01bc4 100644
--- a/js/src/frontend/TreeContext.cpp
+++ b/js/src/frontend/TreeContext.cpp
@@ -30,6 +30,7 @@ frontend::GenerateBlockId(TreeContext *tc, uint32_t &blockid)
         JS_ReportErrorNumber(tc->sc->context, js_GetErrorMessage, NULL, JSMSG_NEED_DIET, "program");
         return false;
     }
+    JS_ASSERT(tc->blockidGen < JS_BIT(20));
     blockid = tc->blockidGen++;
     return true;
 }
diff --git a/js/src/jit-test/tests/basic/testBug773108.js b/js/src/jit-test/tests/basic/testBug773108.js
new file mode 100644
index 000000000000..533ce60f7fa4
--- /dev/null
+++ b/js/src/jit-test/tests/basic/testBug773108.js
@@ -0,0 +1,10 @@
+// |jit-test| error:InternalError
+
+Function("\
+for each(l in[(let(c)([])\
+for each(l in[]))(let(c)w for(u in[]))(let(u)w for(l in[]))(let(c)w for(u in[]))\
+(let(u)w for each(l in[]))(let(c)w for(u in[]))(let(u)w for(l in[]))(let(c)w for(u in[]))\
+(let(l)w for(l in[]))(let(u)w for(l in['']))(let(c)w for(u in[]))(let(u)w for(l in[]))\
+(let(c)w for(l in[]))(let(l)w for(l in[]))(let(c)w for(l in[]))(let(u)w for(l in[]))\
+(let(c)w for(l in[]))(let(u)w for each(l in[x]))(let(w,x)w for(u in[]))]){}\
+")