diff --git a/readme.txt b/readme.txt
index 6bf7d1c..826ffda 100644
--- a/readme.txt
+++ b/readme.txt
@@ -63,6 +63,10 @@ Release notes:
 		Compiler: access predicates consisting of a single multi-query
 		no longer crash the compiler when negated.
 		
+		Compiler: a new --override-serial option makes builds reproducible
+		by overriding the release date and serial number fields. This is
+		not recommended, but occasionally necessary.
+    
 		Compiler: --word-seps option can change which characters are
 		considered word separators (by default . , ; ( ) " * )
 		
diff --git a/src/backend.c b/src/backend.c
index 3d4d824..3e94f9e 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -82,6 +82,7 @@ void usage(char *prgname) {
 	fprintf(stderr, "--strip           -s    Strip internal object names.\n");
 	fprintf(stderr, "--warn-not-topic        Always warn about objects not used as topics.\n");
 	fprintf(stderr, "--no-warn-not-topic     Never warn about objects not used as topics.\n");
+	fprintf(stderr, "--override-serial       Override serial number for reproducible builds.\n");
 	fprintf(stderr, "\n");
 	fprintf(stderr, "Only for z5, z8, or zblorb format:\n");
 	fprintf(stderr, "\n");
@@ -98,8 +99,10 @@ void usage(char *prgname) {
 extern int topic_warning_level; // Defined in frontend.c
 extern int zmachine_optimize_alphabet; // Defined in backend_z.c
 extern int zmachine_preserve_zscii; // Defined in backend_z.c
+static int serial_overridden;
 
 int main(int argc, char **argv) {
+	
 	struct option longopts[] = {
 		{"help", 0, 0, 'h'},
 		{"version", 0, 0, 'V'},
@@ -119,6 +122,7 @@ int main(int argc, char **argv) {
 		{"warn-not-topic", 0, &topic_warning_level, 1},
 		{"no-warn-not-topic", 0, &topic_warning_level, 2},
 		{"optimize-alphabet", 0, &zmachine_optimize_alphabet, 1},
+		{"override-serial", 1, &serial_overridden, 2},
 		{0, 0, 0, 0}
 	};
 
@@ -128,6 +132,7 @@ int main(int argc, char **argv) {
 	char *coverfname = 0;
 	char *coveralt = 0;
 	char *resdir = 0;
+	char *override_serial_with = 0;
 	uint8_t *wordseps = 0;
 	int auxsize = 500, heapsize = 1000, ltssize = 500;
 	int strip = 0;
@@ -146,6 +151,10 @@ int main(int argc, char **argv) {
 		opt = getopt_long(argc, argv, "?hVvo:t:r:c:a:W:H:A:L:s", longopts, 0);
 		switch(opt) {
 			case 0:
+				if(serial_overridden == 2) { // Long-only option with arg
+					override_serial_with = strdup(optarg);
+					serial_overridden = 1;
+				}
 				break; // Added DMS so long-only options are possible
 			case '?':
 			case 'h':
@@ -329,9 +338,26 @@ int main(int argc, char **argv) {
 	} else if(need_meta) {
 		report(LVL_WARN, 0, "No release number declared.");
 	}
-
-	get_timestamp(compiletime_buf, reldate_buf);
-
+	
+	if(serial_overridden) {
+		if(strlen(override_serial_with) != 10) {
+			report(LVL_ERR, 0, "Argument of --override-serial must be exactly 10 characters in the format YYYY-MM-DD");
+			exit(1);
+		}
+		strcpy(reldate_buf, override_serial_with);
+		compiletime_buf[0] = reldate_buf[2]; // yyYy-mm-dd
+		compiletime_buf[1] = reldate_buf[3]; // yyyY-mm-dd
+		compiletime_buf[2] = reldate_buf[5]; // yyyy-Mm-dd
+		compiletime_buf[3] = reldate_buf[6]; // yyyy-mM-dd
+		compiletime_buf[4] = reldate_buf[8]; // yyyy-mm-Dd
+		compiletime_buf[5] = reldate_buf[9]; // yyyy-mm-dD
+		compiletime_buf[6] = 0;
+		report(LVL_WARN, 0, "Release date has been set to \"%s\" and serial number has been set to \"%s\". This is not recommended, and should only be used when necessary for reproducible builds.", reldate_buf, compiletime_buf);
+		free(override_serial_with);
+	} else {
+		get_timestamp(compiletime_buf, reldate_buf);
+	}
+	
 	prg->meta_serial = arena_strdup(&prg->arena, compiletime_buf);
 	prg->meta_reldate = arena_strdup(&prg->arena, reldate_buf);
 
diff --git a/test/simple/warnings/Makefile b/test/simple/warnings/Makefile
index 52ed952..3b75979 100644
--- a/test/simple/warnings/Makefile
+++ b/test/simple/warnings/Makefile
@@ -41,6 +41,9 @@ stdlib.dglib: $(BASEPATH)/stdlib.dg
 
 origin: $(origin)
 
+serial.out: $(BASEPATH)/src/dialogc serial.dg stdlib.dglib
+	$(BASEPATH)/src/dialogc serial.dg stdlib.dglib -t z5 -o serial.z5 --override-serial 0123456789 >serial.out 2>&1 || :
+
 # This one is non-deterministic so we need to sed the results afterward
 ifid.out: $(BASEPATH)/src/dialogc ifid.dg stdlib.dglib
 	$(BASEPATH)/src/dialogc $*.dg stdlib.dglib -t z5 -o ifid.z5 >ifid.out 2>&1 || :
diff --git a/test/simple/warnings/serial.dg b/test/simple/warnings/serial.dg
new file mode 100644
index 0000000..47c2c17
--- /dev/null
+++ b/test/simple/warnings/serial.dg
@@ -0,0 +1,6 @@
+#player
+(current player *)
+(* is #in #room)
+
+#room
+(room *)
diff --git a/test/simple/warnings/serial.gold b/test/simple/warnings/serial.gold
new file mode 100644
index 0000000..f407134
--- /dev/null
+++ b/test/simple/warnings/serial.gold
@@ -0,0 +1 @@
+Warning: Release date has been set to "0123456789" and serial number has been set to "235689". This is not recommended, and should only be used when necessary for reproducible builds.