diff --git a/nimterop/cimport.nim b/nimterop/cimport.nim
index 95004ad..aa7895a 100644
--- a/nimterop/cimport.nim
+++ b/nimterop/cimport.nim
@@ -142,15 +142,35 @@ proc getToast(fullpaths: seq[string], recurse: bool = false, dynlib: string = ""
   for fullpath in fullpaths:
     cmd.add &" {fullpath.sanitizePath}"
 
-  result = if outFile.nBl: fixRelFile(outFile) else:
-    # Generate filename for toast output if not specified
-    getNimteropCacheDir() / "toastCache" / "nimterop_" &
+  let
+    cacheFile = getNimteropCacheDir() / "toastCache" / "nimterop_" &
       ($(cmd & cacheKey).hash().abs()).addFileExt(ext)
 
+  if outFile.nBl:
+    result = fixRelFile(outFile)
+  else:
+    result = cacheFile
+
   when defined(Windows):
     result = result.replace(DirSep, '/')
 
-  if not fileExists(result) or gStateCT.nocache or compileOption("forceBuild"):
+  let
+    # When to regenerate the wrapper
+    regen =
+      if gStateCT.nocache or compileOption("forceBuild"):
+        # No caching or forced
+        true
+      elif not fileExists(result):
+        # Cache or outfile doesn't exist
+        true
+      elif outFile.nBl and (not fileExists(cacheFile) or
+        result.getFileDate() > cacheFile.getFileDate()):
+        # Outfile exists but cache doesn't or outdated
+        true
+      else:
+        false
+
+  if regen:
     let
       dir = result.parentDir()
     if not dirExists(dir):
@@ -160,7 +180,19 @@ proc getToast(fullpaths: seq[string], recurse: bool = false, dynlib: string = ""
 
     var
       (output, ret) = execAction(cmd, die = false)
-    doAssert ret == 0, "\n\n" & (if result.fileExists(): result.readFile() else: "") & output
+    if ret != 0:
+      # If toast fails, print failure to output and delete any generated files
+      let errout = if result.fileExists(): result.readFile() & output else: output
+      rmFile(result)
+      doAssert false, "\n\n" & errout & "\n"
+
+    # Write empty cache file to track changes when outFile specified
+    if outFile.nBl:
+      let dir = cacheFile.parentDir()
+      if not dirExists(dir):
+        mkdir(dir)
+
+      writeFile(cacheFile, "")
 
 macro cOverride*(body): untyped =
   ## When the wrapper code generated by nimterop is missing certain symbols or not
diff --git a/nimterop/toastlib/getters.nim b/nimterop/toastlib/getters.nim
index 8c6abe1..8a4586d 100644
--- a/nimterop/toastlib/getters.nim
+++ b/nimterop/toastlib/getters.nim
@@ -139,7 +139,7 @@ when defined(cpp):
   # not defined in <cwchar> nor any other header).
   type wchar_t* {.importc.} = object
 else:
-  type wchar_t* {.importc, header:"<cwchar>".} = object
+  type wchar_t* {.importc, header:"stddef.h".} = object
 """,
 
     "va_list": """
@@ -417,4 +417,4 @@ proc expandSymlinkAbs*(path: string): string =
     result = path.expandFilename().normalizedPath()
   except:
     result = path
-  result = result.sanitizePath(noQuote = true)
\ No newline at end of file
+  result = result.sanitizePath(noQuote = true)