diff --git a/src/Language/Wasm/Script.hs b/src/Language/Wasm/Script.hs
index 8a585b6..a737605 100644
--- a/src/Language/Wasm/Script.hs
+++ b/src/Language/Wasm/Script.hs
@@ -152,26 +152,29 @@ runScript onAssertFail script = do
         checkModuleInvalid :: Struct.Module -> IO ()
         checkModuleInvalid _ = return ()
 
-        getFailureString :: Validate.ValidationResult -> TL.Text
-        getFailureString (Validate.TypeMismatch _ _) = "type mismatch"
-        getFailureString Validate.ResultTypeDoesntMatch = "type mismatch"
-        getFailureString Validate.MoreThanOneMemory = "multiple memories"
-        getFailureString Validate.MoreThanOneTable = "multiple tables"
-        getFailureString Validate.LocalIndexOutOfRange = "unknown local"
-        getFailureString Validate.MemoryIndexOutOfRange = "unknown memory"
-        getFailureString Validate.TableIndexOutOfRange = "unknown table"
-        getFailureString Validate.FunctionIndexOutOfRange = "unknown function"
-        getFailureString Validate.GlobalIndexOutOfRange = "unknown global"
-        getFailureString Validate.LabelIndexOutOfRange = "unknown label"
-        getFailureString Validate.TypeIndexOutOfRange = "unknown type"
-        getFailureString Validate.MinMoreThanMaxInMemoryLimit = "size minimum must not be greater than maximum"
-        getFailureString Validate.MemoryLimitExceeded = "memory size must be at most 65536 pages (4GiB)"
-        getFailureString Validate.AlignmentOverflow = "alignment must not be larger than natural"
-        getFailureString (Validate.DuplicatedExportNames _) = "duplicate export name"
-        getFailureString Validate.InvalidConstantExpr = "constant expression required"
-        getFailureString Validate.InvalidResultArity = "invalid result arity"
-        -- getFailureString Validate.ImportedGlobalIsNotConst = "global is immutable"
-        getFailureString _ = "not implemented"
+        getFailureString :: Validate.ValidationResult -> [TL.Text]
+        getFailureString (Validate.TypeMismatch _ _) = ["type mismatch"]
+        getFailureString Validate.ResultTypeDoesntMatch = ["type mismatch"]
+        getFailureString Validate.MoreThanOneMemory = ["multiple memories"]
+        getFailureString Validate.MoreThanOneTable = ["multiple tables"]
+        getFailureString Validate.LocalIndexOutOfRange = ["unknown local"]
+        getFailureString Validate.MemoryIndexOutOfRange = ["unknown memory", "unknown memory 0"]
+        getFailureString Validate.TableIndexOutOfRange = ["unknown table", "unknown table 0"]
+        getFailureString Validate.FunctionIndexOutOfRange = ["unknown function", "unknown function 0"]
+        getFailureString Validate.GlobalIndexOutOfRange = ["unknown global"]
+        getFailureString Validate.LabelIndexOutOfRange = ["unknown label"]
+        getFailureString Validate.TypeIndexOutOfRange = ["unknown type"]
+        getFailureString Validate.MinMoreThanMaxInMemoryLimit = ["size minimum must not be greater than maximum"]
+        getFailureString Validate.MemoryLimitExceeded = ["memory size must be at most 65536 pages (4GiB)"]
+        getFailureString Validate.AlignmentOverflow = ["alignment", "alignment must not be larger than natural"]
+        getFailureString (Validate.DuplicatedExportNames _) = ["duplicate export name"]
+        getFailureString Validate.InvalidConstantExpr = ["constant expression required"]
+        getFailureString Validate.InvalidResultArity = ["invalid result arity"]
+        getFailureString Validate.GlobalIsImmutable = ["global is immutable"]
+        getFailureString Validate.ImportedGlobalIsNotConst = ["mutable globals cannot be imported"]
+        getFailureString Validate.ExportedGlobalIsNotConst = ["mutable globals cannot be exported"]
+        getFailureString Validate.InvalidStartFunctionType = ["start function"]
+        getFailureString r = [TL.concat ["not implemented ", (TL.pack $ show r)]]
 
         runAssert :: ScriptState -> Assertion -> IO ()
         runAssert st assert@(AssertReturn action expected) = do
@@ -186,7 +189,7 @@ runScript onAssertFail script = do
             case Validate.validate m of
                 Validate.Valid -> onAssertFail "Invalid module pass validation" assert
                 reason ->
-                    if getFailureString reason == failureString
+                    if failureString `elem` getFailureString reason
                     then return ()
                     else
                         let msg = "Module invalid for other reason. Expected "
diff --git a/src/Language/Wasm/Validate.hs b/src/Language/Wasm/Validate.hs
index 91a86a6..3edeb0f 100644
--- a/src/Language/Wasm/Validate.hs
+++ b/src/Language/Wasm/Validate.hs
@@ -12,7 +12,7 @@ import Language.Wasm.Structure
 import qualified Data.Set as Set
 import Data.List (foldl')
 import qualified Data.Text.Lazy as TL
-import Data.Maybe (fromMaybe, maybeToList, catMaybes, isNothing)
+import Data.Maybe (fromMaybe, maybeToList, catMaybes)
 import Data.Monoid ((<>))
 import Numeric.Natural (Natural)
 
@@ -43,6 +43,8 @@ data ValidationResult =
     | InvalidConstantExpr
     | InvalidStartFunctionType
     | ImportedGlobalIsNotConst
+    | ExportedGlobalIsNotConst
+    | GlobalIsImmutable
     | Valid
     deriving (Show, Eq)
 
@@ -152,6 +154,10 @@ asType :: GlobalType -> VType
 asType (Const v) = Val v
 asType (Mut v) = Val v
 
+shouldBeMut :: GlobalType -> Checker ()
+shouldBeMut (Mut _) = return ()
+shouldBeMut (Const v) = throwError GlobalIsImmutable
+
 getLabel :: LabelIndex -> Checker (Maybe ValueType)
 getLabel lbl = do
     Ctx { labels } <- ask
@@ -202,9 +208,7 @@ getInstrType (BrIf lbl) = do
 getInstrType (BrTable lbls lbl) = do
     r <- getLabel lbl
     rs <- mapM getLabel lbls
-    -- this check for equality doesn't match the spec,
-    -- but a reference compiler does the same
-    if all (\r' -> (isNothing r && isNothing r') || r' == r || isNothing r') rs
+    if all (== r) rs
     then return $ ([Any] ++ (map Val $ maybeToList r) ++ [Val I32]) ==> Any
     else throwError ResultTypeDoesntMatch
 getInstrType Return = do
@@ -218,7 +222,7 @@ getInstrType (CallIndirect sign) = do
     if length tables < 1
     then throwError TableIndexOutOfRange
     else do
-        Arrow from to <- maybeToEither FunctionIndexOutOfRange $ asArrow <$> types !? sign
+        Arrow from to <- maybeToEither TypeIndexOutOfRange $ asArrow <$> types !? sign
         return $ (from ++ [Val I32]) ==> to
 getInstrType Drop = do
     var <- freshVar
@@ -240,11 +244,12 @@ getInstrType (TeeLocal local) = do
     return $ Val t ==> Val t
 getInstrType (GetGlobal global) = do
     Ctx { globals } <- ask
-    t <- maybeToEither LocalIndexOutOfRange $ asType <$> globals !? global
+    t <- maybeToEither GlobalIndexOutOfRange $ asType <$> globals !? global
     return $ empty ==> t
 getInstrType (SetGlobal global) = do
     Ctx { globals } <- ask
-    t <- maybeToEither LocalIndexOutOfRange $ asType <$> globals !? global
+    t <- maybeToEither GlobalIndexOutOfRange $ asType <$> globals !? global
+    shouldBeMut $ globals !! fromIntegral global
     return $ t ==> empty
 getInstrType (I32Load memarg) = do
     checkMemoryInstr 4 memarg
@@ -401,7 +406,7 @@ isConstExpression ((F64Const _):rest) = isConstExpression rest
 isConstExpression ((GetGlobal idx):rest) = do
     Ctx {globals, importedGlobals} <- ask
     if importedGlobals <= idx
-        then throwError InvalidConstantExpr
+        then throwError GlobalIndexOutOfRange
         else return ()
     case globals !! fromIntegral idx of
         Const _ -> isConstExpression rest
@@ -570,7 +575,7 @@ startShouldBeValid m@Module { start = Just (StartFunction idx) } =
     let i = fromIntegral idx in
     if length types > i
     then if FuncType [] [] == types !! i then Valid else InvalidStartFunctionType
-    else TableIndexOutOfRange
+    else FunctionIndexOutOfRange
 
 exportsShouldBeValid :: Validator
 exportsShouldBeValid Module { exports, imports, functions, mems, tables, globals } =
@@ -589,7 +594,17 @@ exportsShouldBeValid Module { exports, imports, functions, mems, tables, globals
         isExportValid (Export _ (ExportMemory memIdx)) =
             if fromIntegral memIdx < length memImports + length mems then Valid else MemoryIndexOutOfRange
         isExportValid (Export _ (ExportGlobal globalIdx)) =
-            if fromIntegral globalIdx < length globalImports + length globals then Valid else GlobalIndexOutOfRange
+            if fromIntegral globalIdx < length globalImports + length globals
+            then (
+                if fromIntegral globalIdx >= length globalImports
+                then (
+                    case globals !! (fromIntegral globalIdx - length globalImports) of
+                        (Global (Mut _) _) -> ExportedGlobalIsNotConst
+                        _ -> Valid
+                )
+                else Valid
+            )
+            else GlobalIndexOutOfRange
 
         areExportNamesUnique :: ValidationResult
         areExportNamesUnique =
diff --git a/tests/Test.hs b/tests/Test.hs
index 9ffdda3..d212491 100644
--- a/tests/Test.hs
+++ b/tests/Test.hs
@@ -34,7 +34,7 @@ compile file = do
 main :: IO ()
 main = do
   files <- Directory.listDirectory "tests/samples"
-  -- let files = ["br_if.wast"]
+  -- let files = ["data.wast"]
   scriptTestCases <- (`mapM` files) $ \file -> do
     content <- LBS.readFile $ "tests/samples/" ++ file
     let Right script = Parser.parseScript <$> Lexer.scanner content