diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index 42cd68ad3..afec57309 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -9428,7 +9428,7 @@ UINT16 P_PartialAddWadFile(const char *wadfilename)
 //	UINT16 mapPos, mapNum = 0;
 
 	// Init file.
-	if ((numlumps = W_InitFile(wadfilename, false, false)) == INT16_MAX)
+	if ((numlumps = W_InitFile(wadfilename, false, false, nullptr)) == INT16_MAX)
 	{
 		refreshdirmenu |= REFRESHDIR_NOTLOADED;
 		return false;
diff --git a/src/w_wad.cpp b/src/w_wad.cpp
index c8218e819..3b3c5020d 100644
--- a/src/w_wad.cpp
+++ b/src/w_wad.cpp
@@ -118,6 +118,10 @@ static FILE *g_shaderspk3file;
 static UINT16 g_shaderspk3numlumps;
 static lumpinfo_t *g_shaderspk3lumps;
 
+#ifndef NOMD5
+static void PrintMD5String(const UINT8 *md5, char *buf);
+#endif
+
 // W_Shutdown
 // Closes all of the WAD files before quitting
 // If not done on a Mac then open wad files
@@ -803,7 +807,7 @@ static UINT16 W_InitFileError (const char *filename, boolean exitworthy)
 //
 // Can now load dehacked files (.soc)
 //
-UINT16 W_InitFile(const char *filename, boolean mainfile, boolean startup)
+UINT16 W_InitFile(const char *filename, boolean mainfile, boolean startup, const char *md5expected)
 {
 	FILE *handle;
 	lumpinfo_t *lumpinfo = NULL;
@@ -862,6 +866,53 @@ UINT16 W_InitFile(const char *filename, boolean mainfile, boolean startup)
 	//
 	W_MakeFileMD5(filename, md5sum);
 
+	if (md5expected)
+	{
+		// moved Graue's <graue@oceanbase.org> W_VerifyFileMD5 inline here
+		UINT8 realmd5[MD5_LEN];
+		INT32 ix;
+
+		I_Assert(strlen(md5expected) == 2*MD5_LEN);
+
+		// Convert an md5 string like "7d355827fa8f981482246d6c95f9bd48"
+		// into a real md5.
+		for (ix = 0; ix < 2*MD5_LEN; ix++)
+		{
+			INT32 n, c = md5expected[ix];
+			if (isdigit(c))
+				n = c - '0';
+			else
+			{
+				I_Assert(isxdigit(c));
+				if (isupper(c)) n = c - 'A' + 10;
+				else n = c - 'a' + 10;
+			}
+			if (ix & 1) realmd5[ix>>1] = (UINT8)(realmd5[ix>>1]+n);
+			else realmd5[ix>>1] = (UINT8)(n<<4);
+		}
+
+		if (memcmp(realmd5, md5sum, 16) != 0)
+		{
+			char actualmd5text[2*MD5_LEN+1];
+			PrintMD5String(md5sum, actualmd5text);
+#ifdef DEVELOP
+			CONS_Printf("File %s does not match expected md5\n", filename);
+#else
+			if (startup)
+			{
+				I_Error(M_GetText("File is old, is corrupt or has been modified: %s (found md5: %s, wanted: %s)\n"), filename, actualmd5text, md5expected);
+			}
+			else
+			{
+				CONS_Alert(CONS_ERROR, M_GetText("Did not load file %s because it did not match expected md5sum %s\n"), filename, md5expected);
+				if (handle)
+					fclose(handle);
+				return W_InitFileError(filename, false);
+			}
+#endif
+		}
+	}
+
 	for (i = 0; i < numwadfiles; i++)
 	{
 		if (!memcmp(wadfiles[i]->md5sum, md5sum, 16))
@@ -1002,7 +1053,7 @@ INT32 W_InitMultipleFiles(char **filenames, boolean addons)
 			G_SetGameModified(true, false);
 
 		//CONS_Debug(DBG_SETUP, "Loading %s\n", *filenames);
-		rc = W_InitFile(*filenames, !addons, true);
+		rc = W_InitFile(*filenames, !addons, true, NULL);
 		if (rc == INT16_MAX)
 			CONS_Printf(M_GetText("Errors occurred while loading %s; not added.\n"), *filenames);
 		overallrc &= (rc != INT16_MAX) ? 1 : 0;
diff --git a/src/w_wad.h b/src/w_wad.h
index 560617d4e..c4185fecd 100644
--- a/src/w_wad.h
+++ b/src/w_wad.h
@@ -145,7 +145,7 @@ void W_Shutdown(void);
 // Opens a WAD file. Returns the FILE * handle for the file, or NULL if not found or could not be opened
 FILE *W_OpenWadFile(const char **filename, boolean useerrors);
 // Load and add a wadfile to the active wad files, returns numbers of lumps, INT16_MAX on error
-UINT16 W_InitFile(const char *filename, boolean mainfile, boolean startup);
+UINT16 W_InitFile(const char *filename, boolean mainfile, boolean startup, const char *md5expected);
 
 // W_InitMultipleFiles returns 1 if all is okay, 0 otherwise,
 // so that it stops with a message if a file was not found, but not if all is okay.