diff --git a/include/nlernd.h b/include/nlernd.h
index 113c789e9..21132ab90 100644
--- a/include/nlernd.h
+++ b/include/nlernd.h
@@ -22,4 +22,7 @@ void nle_get_seed(nle_ctx_t *, unsigned long *, unsigned long *, boolean *,
 /* Fill struct tm with deterministic values from seed via ISAAC64. */
 void nle_fill_fixed_tm(struct tm *, unsigned long);
 
+/* Deterministic ubirthday from seed via ISAAC64. */
+time_t nle_fixed_birthday(unsigned long);
+
 #endif
\ No newline at end of file
diff --git a/src/hacklib.c b/src/hacklib.c
index c0c877fc4..475accd09 100644
--- a/src/hacklib.c
+++ b/src/hacklib.c
@@ -955,7 +955,7 @@ nle_getlt_maybe_fixed()
 int
 getyear()
 {
-    return (1900 + getlt()->tm_year);
+    return (1900 + nle_getlt_maybe_fixed()->tm_year);
 }
 
 #if 0
diff --git a/src/nlernd.c b/src/nlernd.c
index 73892c35f..fdf285ff9 100644
--- a/src/nlernd.c
+++ b/src/nlernd.c
@@ -163,6 +163,27 @@ nle_fill_fixed_tm(struct tm *tm, unsigned long seed)
     tm->tm_yday = tm->tm_mon * 30 + tm->tm_mday;
 }
 
+/*
+ * Deterministic ubirthday derived from the seed. NetHack hashes
+ * ubirthday for between-game flavor variation without consuming game
+ * RNG (shopkeeper names in shknam.c, shop surcharge parity in shk.c,
+ * antholemon() in mkroom.c, scroll labels in read.c), so a wall-clock
+ * ubirthday leaks real time into otherwise fully seeded games.
+ */
+time_t
+nle_fixed_birthday(unsigned long seed)
+{
+    isaac64_ctx time_rng;
+    unsigned char seed_bytes[sizeof(seed)];
+
+    memcpy(seed_bytes, &seed, sizeof(seed_bytes));
+    isaac64_init(&time_rng, seed_bytes, sizeof(seed_bytes));
+
+    /* Arbitrary fixed epoch range: 2000-01-01 plus up to ~40 years. */
+    return (time_t) (946684800UL
+                     + isaac64_next_uint(&time_rng, 1262304000UL));
+}
+
 void
 nle_set_seed(nle_ctx_t *nle, unsigned long core, unsigned long disp,
              boolean reseed, unsigned long lgen)
diff --git a/src/u_init.c b/src/u_init.c
index 77e7445c1..347ae5bf0 100644
--- a/src/u_init.c
+++ b/src/u_init.c
@@ -4,6 +4,10 @@
 /* NetHack may be freely redistributed.  See license for details. */
 
 #include "hack.h"
+#include "nlernd.h"
+#include "nletypes.h"
+
+extern nle_settings settings;
 
 struct trobj {
     short trotyp;
@@ -645,11 +649,16 @@ u_init()
     u.ualignbase[A_CURRENT] = u.ualignbase[A_ORIGINAL] = u.ualign.type =
         aligns[flags.initalign].value;
 
+    if (settings.fix_moon_phase && settings.time_seed_is_set) {
+        /* NLE: pin ubirthday to the seed; see nle_fixed_birthday(). */
+        ubirthday = nle_fixed_birthday(settings.time_seed);
+    } else {
 #if defined(BSD) && !defined(POSIX_TYPES)
-    (void) time((long *) &ubirthday);
+        (void) time((long *) &ubirthday);
 #else
-    (void) time(&ubirthday);
+        (void) time(&ubirthday);
 #endif
+    }
 
     /*
      *  For now, everyone starts out with a night vision range of 1 and