3 files changed, 30 insertions, 0 deletions
diff --git a/src/gamelog.cpp b/src/gamelog.cpp
index 145351ba9..81c4e59fa 100644
--- a/src/gamelog.cpp
+++ b/src/gamelog.cpp
@@ -666,3 +666,30 @@ void GamelogGRFUpdate(const GRFConfig *oldc, const GRFConfig *newc)
 	free(ol);
 	free(nl);
 }
+
+/**
+ * Get the MD5 checksum of the original NewGRF that was loaded.
+ * @param grfid the GRF ID to search for
+ * @param md5sum the MD5 checksum to write to.
+ */
+void GamelogGetOriginalGRFMD5Checksum(uint32 grfid, byte *md5sum)
+{
+	const LoggedAction *la = &_gamelog_action[_gamelog_actions - 1];
+	/* There should always be a "start game" action */
+	assert(_gamelog_actions > 0);
+
+	do {
+		const LoggedChange *lc = &la->change[la->changes - 1];
+		/* There should always be at least one change per action */
+		assert(la->changes > 0);
+
+		do {
+			if (lc->ct == GLCT_GRFADD && lc->grfadd.grfid == grfid) {
+				memcpy(md5sum, lc->grfadd.md5sum, sizeof(lc->grfadd.md5sum));
+				return;
+			}
+		} while (lc-- != la->change);
+	} while (la-- != _gamelog_action);
+
+	NOT_REACHED();
+}
diff --git a/src/gamelog.h b/src/gamelog.h
index d2146d7a3..470a308be 100644
--- a/src/gamelog.h
+++ b/src/gamelog.h
@@ -46,4 +46,6 @@ void GamelogTestGRF();
 
 bool GamelogGRFBugReverse(uint32 grfid, uint16 internal_id);
 
+void GamelogGetOriginalGRFMD5Checksum(uint32 grfid, byte *md5sum);
+
 #endif /* GAMELOG_H */
diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
index 3596f52ec..727440b08 100644
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -617,6 +617,7 @@ struct NewGRFWindow : public Window {
 						ttd_strlcpy(ci->name, c->name != NULL ? c->name : c->filename, lengthof(ci->name));
 						ci->unique_id = BSWAP32(c->grfid);
 						memcpy(ci->md5sum, c->md5sum, sizeof(ci->md5sum));
+						if (HasBit(c->flags, GCF_COMPATIBLE)) GamelogGetOriginalGRFMD5Checksum(c->grfid, ci->md5sum);
 						*cv.Append() = ci;
 					}
 					ShowNetworkContentListWindow(cv.Length() == 0 ? NULL : &cv, CONTENT_TYPE_NEWGRF);