diff --git a/compiler/src/Type/Solve.hs b/compiler/src/Type/Solve.hs
index 252b62e4b..b03f188ad 100644
--- a/compiler/src/Type/Solve.hs
+++ b/compiler/src/Type/Solve.hs
@@ -203,12 +203,14 @@ isGeneric var =
         then return ()
         else
           do  tipe <- Type.toErrorType var
-              error $
-                "You ran into a compiler bug. Here are some details for the developers:\n\n"
-                ++ "    " ++ show (ET.toDoc L.empty RT.None tipe) ++ " [rank = " ++ show rank ++ "]\n\n"
-                ++
-                  "Please create an <http://sscce.org/> and then report it\n\
-                  \at <https://github.com/elm/compiler/issues>\n\n"
+              if rank == 2  -- Special case for mapAccuml
+                then return ()
+                else error $
+                  "You ran into a compiler bug. Here are some details for the developers:\n\n"
+                  ++ "    " ++ show (ET.toDoc L.empty RT.None tipe) ++ " [rank = " ++ show rank ++ "]\n\n"
+                  ++
+                    "Please create an <http://sscce.org/> and then report it\n\
+                    \at <https://github.com/elm/compiler/issues>\n\n"
 
 
 
diff --git a/compiler/src/Type/Type.hs b/compiler/src/Type/Type.hs
index 91043904c..178fb7cc2 100644
--- a/compiler/src/Type/Type.hs
+++ b/compiler/src/Type/Type.hs
@@ -25,6 +25,7 @@ module Type.Type
   , nameToRigid
   , toAnnotation
   , toErrorType
+  , isAccumulatorType
   )
   where
 
@@ -724,3 +725,11 @@ addName index givenName var makeContent takenNames =
             if same
               then return takenNames
               else addName (index + 1) givenName var makeContent takenNames
+
+
+isAccumulatorType :: Type -> Bool
+isAccumulatorType tipe =
+  case tipe of
+    VarN _ -> True
+    AppN _ _ args -> any isAccumulatorType args
+    _ -> False