diff --git a/ShellCheck/AST.hs b/ShellCheck/AST.hs
index 067573b..55c536f 100644
--- a/ShellCheck/AST.hs
+++ b/ShellCheck/AST.hs
@@ -26,6 +26,8 @@ data Id = Id Int deriving (Show, Eq, Ord)
 data Quoted = Quoted | Unquoted deriving (Show, Eq)
 data Dashed = Dashed | Undashed deriving (Show, Eq)
 data AssignmentMode = Assign | Append deriving (Show, Eq)
+data FunctionKeyword = FunctionKeyword Bool deriving (Show, Eq)
+data FunctionParentheses = FunctionParentheses Bool deriving (Show, Eq)
 
 data Token =
     TA_Base Id String Token
@@ -80,7 +82,7 @@ data Token =
     | T_For Id
     | T_ForArithmetic Id Token Token Token [Token]
     | T_ForIn Id String [Token] [Token]
-    | T_Function Id String Token
+    | T_Function Id FunctionKeyword FunctionParentheses String Token
     | T_GREATAND Id
     | T_Glob Id String
     | T_Greater Id
@@ -218,7 +220,7 @@ analyze f g i t =
         return $ T_ForArithmetic id x y z list
 
     delve (T_Script id s l) = dl l $ T_Script id s
-    delve (T_Function id name body) = d1 body $ T_Function id name
+    delve (T_Function id a b name body) = d1 body $ T_Function id a b name
     delve (T_Condition id typ token) = d1 token $ T_Condition id typ
     delve (T_Extglob id str l) = dl l $ T_Extglob id str
     delve (T_DollarBraced id op) = d1 op $ T_DollarBraced id
@@ -308,7 +310,7 @@ getId t = case t of
         T_ForIn id _ _ _  -> id
         T_SelectIn id _ _ _  -> id
         T_CaseExpression id _ _ -> id
-        T_Function id _ _  -> id
+        T_Function id _ _ _ _  -> id
         T_Arithmetic id _  -> id
         T_Script id _ _  -> id
         T_Condition id _ _  -> id
diff --git a/ShellCheck/Analytics.hs b/ShellCheck/Analytics.hs
index dba0e60..fd821bd 100644
--- a/ShellCheck/Analytics.hs
+++ b/ShellCheck/Analytics.hs
@@ -172,6 +172,7 @@ nodeChecks = [
     ,checkCdAndBack
     ,checkWrongArithmeticAssignment
     ,checkConditionalAndOrs
+    ,checkFunctionDeclarations
     ]
 
 
@@ -1884,7 +1885,7 @@ checkFunctionsUsedExternally params t =
 
     analyse f t = snd $ runState (doAnalysis f t) []
     functions = Map.fromList $ analyse findFunctions t
-    findFunctions (T_Function id name _) = modify ((name, id):)
+    findFunctions (T_Function id _ _ name _) = modify ((name, id):)
     findFunctions t@(T_SimpleCommand id _ (_:args))
         | t `isUnqualifiedCommand` "alias" = mapM_ getAlias args
     findFunctions _ = return ()
@@ -2090,6 +2091,25 @@ checkLoopKeywordScope params t |
     subshellType t = case leadType (shellType params) (parentMap params) t of
         NoneScope -> Nothing
         SubshellScope str -> return str
-    isFunction t = case t of T_Function _ _ _ -> True; _ -> False
+    isFunction t = case t of T_Function _ _ _ _ _ -> True; _ -> False
     relevant t = isLoop t || isFunction t || isJust (subshellType t)
 checkLoopKeywordScope _ _ = return ()
+
+
+prop_checkFunctionDeclarations1 = verify checkFunctionDeclarations "#!/bin/ksh\nfunction foo() { command foo --lol \"$@\"; }"
+prop_checkFunctionDeclarations2 = verify checkFunctionDeclarations "#!/bin/dash\nfunction foo { lol; }"
+prop_checkFunctionDeclarations3 = verifyNot checkFunctionDeclarations "foo() { echo bar; }"
+checkFunctionDeclarations params
+        (T_Function id (FunctionKeyword hasKeyword) (FunctionParentheses hasParens) _ _) =
+    case (shellType params) of
+        Bash -> return ()
+        Zsh -> return ()
+        Ksh -> do
+            when (hasKeyword && hasParens) $
+                err id 2111 "ksh does not allow 'function' keyword and '()' at the same time."
+        Sh -> do
+            when (hasKeyword && hasParens) $
+                warn id 2112 "'function' keyword is non-standard. Delete it."
+            when (hasKeyword && not hasParens) $
+                warn id 2113 "'function' keyword is non-standard. Use 'foo()' instead of 'function foo'."
+checkFunctionDeclarations _ _ = return ()
diff --git a/ShellCheck/Parser.hs b/ShellCheck/Parser.hs
index 236265c..5dd6535 100644
--- a/ShellCheck/Parser.hs
+++ b/ShellCheck/Parser.hs
@@ -1580,61 +1580,52 @@ readCaseItem = called "case item" $ do
 
 prop_readFunctionDefinition = isOk readFunctionDefinition "foo() { command foo --lol \"$@\"; }"
 prop_readFunctionDefinition1 = isOk readFunctionDefinition "foo   (){ command foo --lol \"$@\"; }"
-prop_readFunctionDefinition2 = isWarning readFunctionDefinition "function foo() { command foo --lol \"$@\"; }"
-prop_readFunctionDefinition3 = isWarning readFunctionDefinition "function foo { lol; }"
 prop_readFunctionDefinition4 = isWarning readFunctionDefinition "foo(a, b) { true; }"
 prop_readFunctionDefinition5 = isOk readFunctionDefinition ":(){ :|:;}"
 prop_readFunctionDefinition6 = isOk readFunctionDefinition "?(){ foo; }"
 prop_readFunctionDefinition7 = isOk readFunctionDefinition "..(){ cd ..; }"
 prop_readFunctionDefinition8 = isOk readFunctionDefinition "foo() (ls)"
 readFunctionDefinition = called "function" $ do
-    id <- getNextId
-    name <- try readFunctionSignature
+    functionSignature <- try readFunctionSignature
     allspacing
     (disregard (lookAhead $ oneOf "{(") <|> parseProblem ErrorC 1064 "Expected a { to open the function definition.")
     group <- readBraceGroup <|> readSubshell
-    return $ T_Function id name group
-
-
-readFunctionSignature = do
-    readWithFunction <|> readWithoutFunction
+    return $ functionSignature group
   where
-    readWithFunction = do
-        pos <- getPosition
-        try $ do
-            string "function"
-            whitespace
-        parseProblemAt pos InfoC 1005 "Drop the keyword 'function'. It's optional in Bash but invalid in other shells."
-        spacing
-        name <- readFunctionName
-        optional spacing
-        pos <- getPosition
-        readParens <|> do
-            parseProblemAt pos InfoC 1006 "Include '()' after the function name (in addition to dropping 'function')."
-        return name
+    readFunctionSignature = do
+        readWithFunction <|> readWithoutFunction
+      where
+        readWithFunction = do
+            id <- getNextId
+            try $ do
+                string "function"
+                whitespace
+            spacing
+            name <- readFunctionName
+            optional spacing
+            hasParens <- wasIncluded readParens
+            return $ T_Function id (FunctionKeyword True) (FunctionParentheses hasParens) name
 
-    readWithoutFunction = try $ do
-        name <- readFunctionName
-        optional spacing
-        readParens
-        return name
-
-    readParens = do
-        g_Lparen
-        optional spacing
-        g_Rparen <|> do
-            parseProblem ErrorC 1065 "Trying to declare parameters? Don't. Use () and refer to params as $1, $2.."
-            many $ noneOf "\n){"
-            g_Rparen
-        return ()
-
-    readFunctionName = many1 functionChars
+        readWithoutFunction = try $ do
+            id <- getNextId
+            name <- readFunctionName
+            optional spacing
+            readParens
+            return $ T_Function id (FunctionKeyword False) (FunctionParentheses True) name
 
+        readParens = do
+            g_Lparen
+            optional spacing
+            g_Rparen <|> do
+                parseProblem ErrorC 1065 "Trying to declare parameters? Don't. Use () and refer to params as $1, $2.."
+                many $ noneOf "\n){"
+                g_Rparen
+            return ()
 
+        readFunctionName = many1 functionChars
 
 readPattern = (readNormalWord `thenSkip` spacing) `sepBy1` (char '|' `thenSkip` spacing)
 
-
 prop_readCompoundCommand = isOk readCompoundCommand "{ echo foo; }>/dev/null"
 readCompoundCommand = do
     id <- getNextId