diff --git a/src/basic/time-util.c b/src/basic/time-util.c
index a0db97c41a..8d55af8492 100644
--- a/src/basic/time-util.c
+++ b/src/basic/time-util.c
@@ -555,15 +555,29 @@ void dual_timestamp_serialize(FILE *f, const char *name, dual_timestamp *t) {
 
 int dual_timestamp_deserialize(const char *value, dual_timestamp *t) {
         uint64_t a, b;
+        int r, pos;
 
         assert(value);
         assert(t);
 
-        if (sscanf(value, "%" PRIu64 "%" PRIu64, &a, &b) != 2) {
-                log_debug("Failed to parse dual timestamp value \"%s\": %m", value);
+        pos = strspn(value, WHITESPACE);
+        if (value[pos] == '-')
+                return -EINVAL;
+        pos += strspn(value + pos, DIGITS);
+        pos += strspn(value + pos, WHITESPACE);
+        if (value[pos] == '-')
+                return -EINVAL;
+
+        r = sscanf(value, "%" PRIu64 "%" PRIu64 "%n", &a, &b, &pos);
+        if (r != 2) {
+                log_debug("Failed to parse dual timestamp value \"%s\".", value);
                 return -EINVAL;
         }
 
+        if (value[pos] != '\0')
+                /* trailing garbage */
+                return -EINVAL;
+
         t->realtime = a;
         t->monotonic = b;
 
diff --git a/src/test/test-time.c b/src/test/test-time.c
index 911282bf0c..c9e31e90e1 100644
--- a/src/test/test-time.c
+++ b/src/test/test-time.c
@@ -273,6 +273,43 @@ static void test_format_timestamp_utc(void) {
         test_format_timestamp_utc_one(USEC_INFINITY, NULL);
 }
 
+static void test_dual_timestamp_deserialize(void) {
+        int r;
+        dual_timestamp t;
+
+        r = dual_timestamp_deserialize("1234 5678", &t);
+        assert_se(r == 0);
+        assert_se(t.realtime == 1234);
+        assert_se(t.monotonic == 5678);
+
+        r = dual_timestamp_deserialize("1234x 5678", &t);
+        assert_se(r == -EINVAL);
+
+        r = dual_timestamp_deserialize("1234 5678y", &t);
+        assert_se(r == -EINVAL);
+
+        r = dual_timestamp_deserialize("-1234 5678", &t);
+        assert_se(r == -EINVAL);
+
+        r = dual_timestamp_deserialize("1234 -5678", &t);
+        assert_se(r == -EINVAL);
+
+        /* Check that output wasn't modified. */
+        assert_se(t.realtime == 1234);
+        assert_se(t.monotonic == 5678);
+
+        r = dual_timestamp_deserialize("+123 567", &t);
+        assert_se(r == 0);
+        assert_se(t.realtime == 123);
+        assert_se(t.monotonic == 567);
+
+        /* Check that we get "infinity" on overflow. */
+        r = dual_timestamp_deserialize("18446744073709551617 0", &t);
+        assert_se(r == 0);
+        assert_se(t.realtime == USEC_INFINITY);
+        assert_se(t.monotonic == 0);
+}
+
 int main(int argc, char *argv[]) {
         uintmax_t x;
 
@@ -288,6 +325,7 @@ int main(int argc, char *argv[]) {
         test_usec_sub();
         test_format_timestamp();
         test_format_timestamp_utc();
+        test_dual_timestamp_deserialize();
 
         /* Ensure time_t is signed */
         assert_cc((time_t) -1 < (time_t) 1);