diff --git a/src/Tokstyle/C/Linter/VoidCall.hs b/src/Tokstyle/C/Linter/VoidCall.hs
index 6534867..efea9fa 100644
--- a/src/Tokstyle/C/Linter/VoidCall.hs
+++ b/src/Tokstyle/C/Linter/VoidCall.hs
@@ -48,6 +48,7 @@ linter :: AstActions (TravT Env Identity)
 linter = astActions
     { doIdentDecl = \node act -> case node of
         FunctionDef (FunDef (VarDecl (VarName fname _) _ (FunctionType (FunType _ ps _) _)) (CCompound _ body _) _)
+            | "os_" `isPrefixOf` idName fname -> return ()
             | "sys_" `isPrefixOf` idName fname -> return ()
             | otherwise -> checkFunction (voidPtrParams ps) body
 
diff --git a/src/Tokstyle/C/Patterns.hs b/src/Tokstyle/C/Patterns.hs
index c366ecf..d0d0500 100644
--- a/src/Tokstyle/C/Patterns.hs
+++ b/src/Tokstyle/C/Patterns.hs
@@ -5,6 +5,14 @@
 {- HLINT ignore "Use camelCase" -}
 module Tokstyle.C.Patterns where
 
+import           Language.C                    (CConstant (CIntConst),
+                                                CDeclaration (CDecl),
+                                                CDeclarationSpecifier (CTypeSpec),
+                                                CDeclarator (CDeclr),
+                                                CDerivedDeclarator (CPtrDeclr),
+                                                CExpression (CCast, CConst),
+                                                CInteger (CInteger),
+                                                CTypeSpecifier (CVoidType))
 import           Language.C.Analysis.SemRep    (CompTypeRef (..), IntType (..),
                                                 Type (..), TypeDefRef (..),
                                                 TypeName (..))
@@ -25,6 +33,8 @@ pattern TY_sockaddr_in_ptr      <- TY_struct_ptr "sockaddr_in"
 pattern TY_sockaddr_in6_ptr     <- TY_struct_ptr "sockaddr_in6"
 pattern TY_canon_bool           <- (canonicalType -> DirectType (TyIntegral TyBool) _ _)
 
+pattern E_0 <- CConst (CIntConst (CInteger 0 _ _) _)
+pattern E_nullptr <- CCast (CDecl [CTypeSpec (CVoidType _)] [(Just (CDeclr _ [CPtrDeclr [] _] _ _ _),_,_)] _) E_0 _
 
 isEnum :: Type -> Bool
 isEnum (canonicalType -> DirectType TyEnum{} _ _) = True
diff --git a/src/Tokstyle/Linter/DeclsHaveDefns.hs b/src/Tokstyle/Linter/DeclsHaveDefns.hs
index cbe4854..1402ff4 100644
--- a/src/Tokstyle/Linter/DeclsHaveDefns.hs
+++ b/src/Tokstyle/Linter/DeclsHaveDefns.hs
@@ -19,7 +19,6 @@ import           Language.Cimple             (AlexPosn (..), Lexeme (..),
 import qualified Language.Cimple.Diagnostics as Diagnostics
 import           Language.Cimple.TraverseAst (AstActions, astActions, doNode,
                                               traverseAst)
-import           System.FilePath             (takeFileName)
 import           Text.EditDistance           (defaultEditCosts,
                                               levenshteinDistance)
 
@@ -77,7 +76,6 @@ analyse =
     . Map.elems
     . flip State.execState empty
     . traverseAst collectPairs
-    . filter (not . (`elem` ["tox.h", "tox_private.h"]) . takeFileName . fst)
   where
     lacksDefn DeclDefn{decl, defn = Nothing} = decl
     lacksDefn _                              = Nothing