diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index c9a78be9f..a86c8a955 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -42,6 +42,11 @@
 
 __BEGIN_DECLS
 
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnullability-completeness"
+#endif
+
 wint_t            btowc(int);
 int               fwprintf(FILE *, const wchar_t *, ...);
 int               fwscanf(FILE *, const wchar_t *, ...);
@@ -134,6 +139,10 @@ FILE* open_wmemstream(wchar_t**, size_t*) __INTRODUCED_IN(23);
 wchar_t* wcsdup(const wchar_t*);
 size_t wcsnlen(const wchar_t*, size_t);
 
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+
 __END_DECLS
 
 #endif /* _WCHAR_H_ */
diff --git a/tools/versioner/src/Driver.cpp b/tools/versioner/src/Driver.cpp
index 1b631b6ed..a09481838 100644
--- a/tools/versioner/src/Driver.cpp
+++ b/tools/versioner/src/Driver.cpp
@@ -100,11 +100,12 @@ static void generateTargetCC1Flags(llvm::IntrusiveRefCntPtr<clang::vfs::FileSyst
   std::vector<std::string> cmd = { "versioner" };
   cmd.push_back("-std=c11");
   cmd.push_back("-x");
-  cmd.push_back("c-header");
+  cmd.push_back("c");
   cmd.push_back("-fsyntax-only");
 
   cmd.push_back("-Wall");
   cmd.push_back("-Wextra");
+  cmd.push_back("-Weverything");
   cmd.push_back("-Werror");
   cmd.push_back("-Wundef");
   cmd.push_back("-Wno-unused-macros");
@@ -134,7 +135,9 @@ static void generateTargetCC1Flags(llvm::IntrusiveRefCntPtr<clang::vfs::FileSyst
     cmd.push_back(dir);
   }
 
+  cmd.push_back("-include");
   cmd.push_back(filename_placeholder);
+  cmd.push_back("-");
 
   auto diags = constructDiags();
   driver::Driver driver("versioner", llvm::sys::getDefaultTargetTriple(), *diags, vfs);
diff --git a/tools/versioner/src/versioner.cpp b/tools/versioner/src/versioner.cpp
index 735ea04e9..747c767d5 100644
--- a/tools/versioner/src/versioner.cpp
+++ b/tools/versioner/src/versioner.cpp
@@ -18,6 +18,7 @@
 #include <err.h>
 #include <limits.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
@@ -190,6 +191,21 @@ static std::unique_ptr<HeaderDatabase> compileHeaders(const std::set<Compilation
     }
   }
 
+  // Dup an empty file to stdin, so that we can use `clang -include a.h -` instead of `clang a.h`,
+  // since some warnings don't get generated in files that are compiled directly.
+  FILE* empty_file = tmpfile();
+  if (!empty_file) {
+    err(1, "failed to create temporary file");
+  }
+
+  int empty_file_fd = fileno(empty_file);
+  if (empty_file_fd == -1) {
+    errx(1, "fileno failed on tmpfile");
+  }
+
+  dup2(empty_file_fd, STDIN_FILENO);
+  fclose(empty_file);
+
   thread_count = std::min(thread_count, jobs.size());
 
   if (thread_count == 1) {