diff --git a/qa/src/GNUlocaldefs b/qa/src/GNUlocaldefs
index 48b6e3a685..80ff52c564 100644
--- a/qa/src/GNUlocaldefs
+++ b/qa/src/GNUlocaldefs
@@ -56,7 +56,8 @@ CFILES = disk_test.c exercise.c context_test.c chkoptfetch.c \
 	throttle.c throttle_timeout.c y2038.c bigpmcdpmids.c pdu-gadget.c \
 	strnfoo.c mmv_ondisk.c newcontext.c api_abi.c interp_bug3.c \
 	pmsetmode.c scanindex.c localtime.c httpcache.c unregister.c \
-	genpmns.c
+	genpmns.c \
+	series_time_parse_test.c
 
 ifeq ($(shell test -f ../localconfig && echo 1), 1)
 include ../localconfig
@@ -486,6 +487,10 @@ genpmns:	genpmns.c
 	rm -f $@
 	$(CCF) $(CDEFS) -o $@ $< $(LDLIBS)
 
+series_time_parse_test:	series_time_parse_test.c libpcp.h
+	rm -f $@
+	$(CCF) $(CDEFS) -o $@ $< $(LDLIBS)
+
 # --- need libpcp but different versions of PMAPI_VERSION and/or
 #     libpcp.$(DSOSUFFIX)
 #
@@ -938,6 +943,7 @@ qa_libpcp_compat.o:	libpcp.h
 qa_timezone.o:	libpcp.h
 recon.o:	libpcp.h
 rtimetest.o:	libpcp.h
+series_time_parse_test.o:	libpcp.h
 slow_af.o:	libpcp.h
 sortinst.o:	libpcp.h
 store.o:	libpcp.h
diff --git a/qa/src/series_time_parse_test.c b/qa/src/series_time_parse_test.c
new file mode 100644
index 0000000000..6f28cdcf5d
--- /dev/null
+++ b/qa/src/series_time_parse_test.c
@@ -0,0 +1,219 @@
+/*
+ * Copyright (c) 2024 Red Hat.
+ *
+ * Unit tests for pmproxy series API time parsing, covering the bugs
+ * reported in issue #2503:
+ *
+ *  - Tier 1/2: negative relative offsets ("-30s", "-2m", "-1h", "-7d")
+ *    fail when end sentinel is PM_MAX_TIME_T (the old broken behaviour).
+ *    They MUST succeed when end is the current wall clock time.
+ *
+ *  - Tier 3: __pmtimespecParse() with an ISO-8601+Z string must not
+ *    crash; it may return success or failure, but the process must live.
+ *
+ * These are UNIT tests — no Redis, no pmcd, no network required.
+ * Exit 0 on success, non-zero if any assertion fails.
+ *
+ * This library is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <pcp/pmapi.h>
+#include "libpcp.h"
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+static int failures = 0;
+static int passes = 0;
+
+#define CHECK(expr, msg) \
+    do { \
+	if (!(expr)) { \
+	    fprintf(stderr, "FAIL [%s:%d]: %s\n", __FILE__, __LINE__, (msg)); \
+	    failures++; \
+	} else { \
+	    printf("PASS: %s\n", (msg)); \
+	    passes++; \
+	} \
+    } while (0)
+
+/*
+ * Attempt to parse a relative-time string using the given end boundary.
+ * Returns the parsed timespec, or {-1, 0} on parse failure.
+ */
+static struct timespec
+parse_with_end(const char *str, struct timespec *end)
+{
+    struct timespec	start = { 0, 0 };
+    struct timespec	result = { -1, 0 };
+    char		*errmsg = NULL;
+
+    if (__pmtimespecParse(str, &start, end, &result, &errmsg) < 0) {
+	if (errmsg) free(errmsg);
+	result.tv_sec = -1;
+    }
+    return result;
+}
+
+/*
+ * Confirm that parsing fails with the PM_MAX_TIME_T sentinel — this
+ * documents the pre-fix broken behaviour and ensures the test itself
+ * is actually testing something meaningful.
+ */
+static void
+test_broken_sentinel_rejects_negative_offsets(void)
+{
+    struct timespec	broken_end = { PM_MAX_TIME_T, 0 };
+    struct timespec	result;
+
+    printf("\n--- Bug demonstration: PM_MAX_TIME_T sentinel breaks negative offsets ---\n");
+
+    result = parse_with_end("-30s", &broken_end);
+    CHECK(result.tv_sec < 0,
+	  "-30s fails with PM_MAX_TIME_T end sentinel (pre-fix behaviour)");
+
+    result = parse_with_end("-7d", &broken_end);
+    CHECK(result.tv_sec < 0,
+	  "-7d fails with PM_MAX_TIME_T end sentinel (pre-fix behaviour)");
+}
+
+/*
+ * Confirm that negative relative offsets succeed when end=now — this is
+ * the correct behaviour the fix to parsetime() in query.c enables.
+ */
+static void
+test_negative_offsets_succeed_with_now_end(struct timespec *now)
+{
+    struct timespec	result;
+    time_t		expected;
+
+    printf("\n--- Fix verification: negative offsets work when end=now ---\n");
+
+    /* -30s: result should be now minus 30 seconds */
+    result = parse_with_end("-30s", now);
+    CHECK(result.tv_sec > 0, "-30s parses without error when end=now");
+    expected = now->tv_sec - 30;
+    CHECK(result.tv_sec >= expected - 1 && result.tv_sec <= expected + 1,
+	  "-30s result is approximately 30 seconds before now");
+
+    /* -2m: result should be now minus 120 seconds */
+    result = parse_with_end("-2m", now);
+    CHECK(result.tv_sec > 0, "-2m parses without error when end=now");
+    expected = now->tv_sec - 120;
+    CHECK(result.tv_sec >= expected - 1 && result.tv_sec <= expected + 1,
+	  "-2m result is approximately 2 minutes before now");
+
+    /* -1h: result should be now minus 3600 seconds */
+    result = parse_with_end("-1h", now);
+    CHECK(result.tv_sec > 0, "-1h parses without error when end=now");
+    expected = now->tv_sec - 3600;
+    CHECK(result.tv_sec >= expected - 1 && result.tv_sec <= expected + 1,
+	  "-1h result is approximately 1 hour before now");
+
+    /* -7d: result should be now minus 7 * 86400 seconds */
+    result = parse_with_end("-7d", now);
+    CHECK(result.tv_sec > 0, "-7d parses without error when end=now");
+    expected = now->tv_sec - (7 * 86400);
+    CHECK(result.tv_sec >= expected - 1 && result.tv_sec <= expected + 1,
+	  "-7d result is approximately 7 days before now");
+}
+
+/*
+ * Positive relative offsets should still work — they're relative to start
+ * regardless of the end sentinel.
+ */
+static void
+test_positive_offsets_still_work(struct timespec *now)
+{
+    struct timespec	start = { 0, 0 };
+    struct timespec	result;
+    char		*errmsg = NULL;
+
+    printf("\n--- Positive relative offsets (regression) ---\n");
+
+    /* +30s relative to epoch zero = exactly 30 seconds */
+    if (__pmtimespecParse("+30s", &start, now, &result, &errmsg) == 0) {
+	CHECK(result.tv_sec == 30, "+30s from epoch yields tv_sec == 30");
+    } else {
+	CHECK(0, "+30s should parse successfully");
+	if (errmsg) free(errmsg);
+    }
+
+    /* bare "30s" is also a positive offset */
+    if (__pmtimespecParse("30s", &start, now, &result, &errmsg) == 0) {
+	CHECK(result.tv_sec == 30, "30s (no sign) from epoch yields tv_sec == 30");
+    } else {
+	CHECK(0, "30s should parse successfully");
+	if (errmsg) free(errmsg);
+    }
+}
+
+/*
+ * ISO-8601 with Z suffix — must not crash.  The exact return value
+ * depends on getdate grammar support, which is fine; survival is mandatory.
+ */
+static void
+test_iso8601_z_suffix_does_not_crash(struct timespec *now)
+{
+    struct timespec	start = { 0, 0 };
+    struct timespec	result = { -1, 0 };
+    char		*errmsg = NULL;
+    int			sts;
+
+    printf("\n--- ISO-8601 with Z suffix (crash safety) ---\n");
+
+    sts = __pmtimespecParse("2024-01-15T10:30:00Z", &start, now, &result, &errmsg);
+    printf("INFO: __pmtimespecParse(\"2024-01-15T10:30:00Z\") returned %d\n", sts);
+    if (errmsg) { free(errmsg); errmsg = NULL; }
+
+    /* If we reach this line, no crash — that's the pass condition */
+    CHECK(1, "2024-01-15T10:30:00Z did not crash __pmtimespecParse");
+
+    /* Malformed input must return error without crashing */
+    sts = __pmtimespecParse("not-a-date", &start, now, &result, &errmsg);
+    CHECK(sts < 0, "\"not-a-date\" returns error from __pmtimespecParse");
+    if (errmsg) free(errmsg);
+}
+
+int
+main(int argc, char *argv[])
+{
+    struct timespec	now;
+    int			c, errflag = 0;
+
+    pmSetProgname(argv[0]);
+
+    while ((c = getopt(argc, argv, "D:?")) != EOF) {
+	switch (c) {
+	case 'D':
+	    if (pmSetDebug(optarg) < 0) {
+		fprintf(stderr, "%s: unrecognized debug options (%s)\n",
+			pmGetProgname(), optarg);
+		errflag++;
+	    }
+	    break;
+	default:
+	    errflag++;
+	    break;
+	}
+    }
+
+    if (errflag) {
+	fprintf(stderr, "Usage: %s [-D debug]\n", pmGetProgname());
+	return 1;
+    }
+
+    pmtimespecNow(&now);
+    printf("series_time_parse_test: now = %ld\n", (long)now.tv_sec);
+
+    test_broken_sentinel_rejects_negative_offsets();
+    test_negative_offsets_succeed_with_now_end(&now);
+    test_positive_offsets_still_work(&now);
+    test_iso8601_z_suffix_does_not_crash(&now);
+
+    printf("\n=== Results: %d passed, %d failed ===\n", passes, failures);
+    return failures ? 1 : 0;
+}
diff --git a/src/libpcp_web/src/query.c b/src/libpcp_web/src/query.c
index 29f2ac0adf..ab5f0ff8b7 100644
--- a/src/libpcp_web/src/query.c
+++ b/src/libpcp_web/src/query.c
@@ -6333,11 +6333,12 @@ static void
 parsetime(seriesQueryBaton *baton, sds string, struct timespec *result, const char *source)
 {
     struct timespec	start = { 0, 0 };
-    struct timespec	end = { PM_MAX_TIME_T, 0 };
+    struct timespec	end;	/* wall clock — enables negative-relative branch */
     char		*error;
     sds			msg;
     int			sts;
 
+    pmtimespecNow(&end);
     if ((sts = __pmtimespecParse(string, &start, &end, result, &error)) < 0) {
 	msg = NULL;
 	infofmt(msg, "Cannot parse time %s with %s:\n%s",
@@ -6484,6 +6485,12 @@ pmSeriesValues(pmSeriesSettings *settings, pmSeriesTimeWindow *timing,
 	return -ENOMEM;
     initSeriesQueryBaton(baton, settings, arg);
     initSeriesGetValues(baton, nseries, series, timing);
+    if (baton->error) {
+	/* parse error or alloc failure — abort before launching async phases */
+	int sts = baton->error;
+	series_query_finished(baton);
+	return sts;
+    }
 
     baton->current = &baton->phases[0];
     baton->phases[i++].func = series_lookup_services;