diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index 6230f5b..78b5366 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -484,7 +484,7 @@ checkShebang params (T_Annotation _ list t) =
 checkShebang params (T_Script id sb _) = execWriter $ do
     unless (shellTypeSpecified params) $ do
         when (sb == "") $
-            err id 2148 "Tips depend on target shell and yours is unknown. Add a shebang."
+            err id 2148 "Tips depend on target shell and yours is unknown. Add a shebang or a .bash, .ksh, .dash extension to the filename."
         when (executableFromShebang sb == "ash") $
             warn id 2187 "Ash scripts will be checked as Dash. Add '# shellcheck shell=dash' to silence."
     unless (null sb) $ do
diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index 37a96ad..b2b4edd 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -175,7 +175,7 @@ makeCommentWithFix severity id code str fix =
 makeParameters spec =
     let params = Parameters {
         rootNode = root,
-        shellType = fromMaybe (determineShell root) $ asShellType spec,
+        shellType = fromMaybe (determineShell (asFallbackShell spec) root) $ asShellType spec,
         hasSetE = containsSetE root,
         hasLastpipe =
             case shellType params of
@@ -184,7 +184,7 @@ makeParameters spec =
                 Sh   -> False
                 Ksh  -> True,
 
-        shellTypeSpecified = isJust $ asShellType spec,
+        shellTypeSpecified = isJust (asShellType spec) || isJust (asFallbackShell spec),
         parentMap = getParentTree root,
         variableFlow = getVariableFlow params root,
         tokenPositions = asTokenPositions spec
@@ -227,11 +227,13 @@ prop_determineShell4 = determineShellTest "#!/bin/ksh\n#shellcheck shell=sh\nfoo
 prop_determineShell5 = determineShellTest "#shellcheck shell=sh\nfoo" == Sh
 prop_determineShell6 = determineShellTest "#! /bin/sh" == Sh
 prop_determineShell7 = determineShellTest "#! /bin/ash" == Dash
+prop_determineShell8 = determineShellTest' (Just Ksh) "#!/bin/sh" == Sh
 
-determineShellTest = determineShell . fromJust . prRoot . pScript
-determineShell t = fromMaybe Bash $ do
+determineShellTest = determineShellTest' Nothing
+determineShellTest' fallbackShell = determineShell fallbackShell . fromJust . prRoot . pScript
+determineShell fallbackShell t = fromMaybe Bash $ do
     shellString <- foldl mplus Nothing $ getCandidates t
-    shellForExecutable shellString
+    shellForExecutable shellString `mplus` fallbackShell
   where
     forAnnotation t =
         case t of
diff --git a/src/ShellCheck/Checker.hs b/src/ShellCheck/Checker.hs
index 10074e3..ac51ddd 100644
--- a/src/ShellCheck/Checker.hs
+++ b/src/ShellCheck/Checker.hs
@@ -48,6 +48,16 @@ tokenToPosition startMap t = fromMaybe fail $ do
   where
     fail = error "Internal shellcheck error: id doesn't exist. Please report!"
 
+shellFromFilename filename = foldl mplus Nothing candidates
+  where
+    shellExtensions = [(".ksh", Ksh)
+                      ,(".bash", Bash)
+                      ,(".dash", Dash)]
+                      -- The `.sh` is too generic to determine the shell:
+                      -- We fallback to Bash in this case and emit SC2148 if there is no shebang
+    candidates =
+        map (\(ext,sh) -> if ext `isSuffixOf` filename then Just sh else Nothing) shellExtensions
+
 checkScript :: Monad m => SystemInterface m -> CheckSpec -> m CheckResult
 checkScript sys spec = do
     results <- checkScript (csScript spec)
@@ -69,6 +79,7 @@ checkScript sys spec = do
                 as {
                     asScript = root,
                     asShellType = csShellTypeOverride spec,
+                    asFallbackShell = shellFromFilename $ csFilename spec,
                     asCheckSourced = csCheckSourced spec,
                     asExecutionMode = Executed,
                     asTokenPositions = tokenPositions
diff --git a/src/ShellCheck/Interface.hs b/src/ShellCheck/Interface.hs
index dd53f6f..285042f 100644
--- a/src/ShellCheck/Interface.hs
+++ b/src/ShellCheck/Interface.hs
@@ -25,7 +25,7 @@ module ShellCheck.Interface
     , CheckResult(crFilename, crComments)
     , ParseSpec(psFilename, psScript, psCheckSourced, psShellTypeOverride)
     , ParseResult(prComments, prTokenPositions, prRoot)
-    , AnalysisSpec(asScript, asShellType, asExecutionMode, asCheckSourced, asTokenPositions)
+    , AnalysisSpec(asScript, asShellType, asFallbackShell, asExecutionMode, asCheckSourced, asTokenPositions)
     , AnalysisResult(arComments)
     , FormatterOptions(foColorOption, foWikiLinkCount)
     , Shell(Ksh, Sh, Bash, Dash)
@@ -138,6 +138,7 @@ newParseResult = ParseResult {
 data AnalysisSpec = AnalysisSpec {
     asScript :: Token,
     asShellType :: Maybe Shell,
+    asFallbackShell :: Maybe Shell,
     asExecutionMode :: ExecutionMode,
     asCheckSourced :: Bool,
     asTokenPositions :: Map.Map Id (Position, Position)
@@ -146,6 +147,7 @@ data AnalysisSpec = AnalysisSpec {
 newAnalysisSpec token = AnalysisSpec {
     asScript = token,
     asShellType = Nothing,
+    asFallbackShell = Nothing,
     asExecutionMode = Executed,
     asCheckSourced = False,
     asTokenPositions = Map.empty