diff --git a/test/hill.cc b/test/hill.cc
index a3152868..1b03ddf0 100644
--- a/test/hill.cc
+++ b/test/hill.cc
@@ -65,8 +65,10 @@ bool testcase_hill::run() {
 
   while (should_continue()) {
     const keygen::serial_t a_serial = serial_count;
-    if (unlikely(!keyvalue_maker.increment(serial_count, 1)))
-      failure("uphill: unexpected key-space overflow");
+    if (unlikely(!keyvalue_maker.increment(serial_count, 1))) {
+      log_notice("uphill: unexpected key-space overflow");
+      break;
+    }
 
     const keygen::serial_t b_serial = serial_count;
     assert(b_serial > a_serial);
@@ -186,7 +188,7 @@ bool testcase_hill::run() {
     }
   }
 
-  while (serial_count > 0) {
+  while (serial_count > 1) {
     if (unlikely(!keyvalue_maker.increment(serial_count, -2)))
       failure("downhill: unexpected key-space underflow");
 
diff --git a/test/keygen.cc b/test/keygen.cc
index 30cdf7a5..0110b049 100644
--- a/test/keygen.cc
+++ b/test/keygen.cc
@@ -184,7 +184,8 @@ bool maker::increment(serial_t &serial, int delta) const {
   }
 
   serial_t target = serial + (int64_t)delta;
-  if (target > mask(mapping.width)) {
+  if (target > mask(mapping.width) ||
+      ((delta > 0) ? target < serial : target > serial)) {
     log_extra("keygen-increment: %" PRIu64 "%-d => %" PRIu64 ", overflow",
               serial, delta, target);
     return false;
diff --git a/test/ttl.cc b/test/ttl.cc
index 2b259ba8..b98f4a8b 100644
--- a/test/ttl.cc
+++ b/test/ttl.cc
@@ -132,8 +132,10 @@ bool testcase_ttl::run() {
         failure_perror("mdbx_put(head)", err);
       }
 
-      if (unlikely(!keyvalue_maker.increment(serial, 1)))
-        failure("uphill: unexpected key-space overflow");
+      if (unlikely(!keyvalue_maker.increment(serial, 1))) {
+        log_notice("ttl: unexpected key-space overflow");
+        goto bailout;
+      }
     }
     err = breakable_restart();
     if (unlikely(err != MDBX_SUCCESS)) {