diff --git a/src/scheduler/src/repl_break.c b/src/scheduler/src/repl_break.c
index 92742701..4ddc476d 100644
--- a/src/scheduler/src/repl_break.c
+++ b/src/scheduler/src/repl_break.c
@@ -548,12 +548,28 @@ bool repl_cmd_delete(xce_sched_sim_driver_t* sim, const char* line)
     }
 
     {
-        int id = atoi(tokens[1]);
+        /* strtol()+endptr, not atoi() -- same "fail loud" discipline
+         * repl.c's repl_cmd_step() doc comment establishes: atoi() would
+         * silently coerce a non-numeric token (e.g. a typo'd id) to 0
+         * rather than reporting the input as invalid, misreporting a bad
+         * argument as "no breakpoint with id 0". Breakpoint ids are
+         * assigned via pre-incremented next_bp_id (repl_cmd_break(), this
+         * file), so 1 is the smallest id that can ever legitimately exist. */
+        long  id;
+        char* endptr;
 
-        if (!repl_breakpoint_remove(sim->repl_state, id)) {
-            fprintf(stdout, "[sim] delete: no breakpoint with id %d\n", id);
+        id = strtol(tokens[1], &endptr, 10);
+        if ((endptr == tokens[1]) || (*endptr != '\0') || (id <= 0)) {
+            fprintf(stdout,
+                  "[sim] delete: '%s' is not a valid breakpoint id -- usage: "
+                  "delete <id>|all\n", tokens[1]);
+            return false;
+        }
+
+        if (!repl_breakpoint_remove(sim->repl_state, (int)id)) {
+            fprintf(stdout, "[sim] delete: no breakpoint with id %ld\n", id);
         } else {
-            fprintf(stdout, "[sim] breakpoint %d deleted\n", id);
+            fprintf(stdout, "[sim] breakpoint %ld deleted\n", id);
         }
     }
 
diff --git a/src/scheduler/testsuite/test_repl_breakpoints_inspection.c b/src/scheduler/testsuite/test_repl_breakpoints_inspection.c
index 8a60b8a2..4f9e8ba9 100644
--- a/src/scheduler/testsuite/test_repl_breakpoints_inspection.c
+++ b/src/scheduler/testsuite/test_repl_breakpoints_inspection.c
@@ -420,6 +420,44 @@ static void test_delete_all_removes_all_breakpoints(void)
     printf("test_delete_all_removes_all_breakpoints: PASS\n");
 }
 
+static void test_delete_non_numeric_id_rejected(void)
+{
+    xce_sched_sim_driver_t sim;
+
+    memset(&sim, 0, sizeof(sim));
+    /* xce_sched_core_init() is the same precondition xce_repl_start()
+     * always has satisfied for it in the real driver flow (sched_sim_driver_start()
+     * runs first) -- it also transitively calls xstring_table_init()
+     * (core.c), which makeString() (breakpoint token/filter string copies,
+     * repl_break.c) requires to not silently return NULL. */
+    TEST_ASSERT_EQUAL_INT(0, xce_sched_core_init(&(sim.core)));
+    sim.repl_state = repl_state_ensure(&sim);
+    TEST_ASSERT_NOT_NULL(sim.repl_state);
+
+    TEST_ASSERT_FALSE(repl_dispatch(&sim, "break JOB_PUSH"));
+    TEST_ASSERT_EQUAL_INT(1, sim.repl_state->nbreakpoints);
+
+    /* "abc" must be rejected outright, not silently coerced to id 0
+     * (atoi()'s old behavior) and reported as "no breakpoint with id 0". */
+    TEST_ASSERT_FALSE(repl_dispatch(&sim, "delete abc"));
+    TEST_ASSERT_EQUAL_INT(1, sim.repl_state->nbreakpoints);
+
+    /* "0" and negative ids can never be legitimately assigned
+     * (repl_cmd_break()'s pre-incremented next_bp_id starts at 1) -- also
+     * rejected as invalid, not treated as a well-formed-but-missing id. */
+    TEST_ASSERT_FALSE(repl_dispatch(&sim, "delete 0"));
+    TEST_ASSERT_EQUAL_INT(1, sim.repl_state->nbreakpoints);
+    TEST_ASSERT_FALSE(repl_dispatch(&sim, "delete -1"));
+    TEST_ASSERT_EQUAL_INT(1, sim.repl_state->nbreakpoints);
+
+    /* trailing garbage after a numeric prefix ("1x") is also rejected, not
+     * truncated down to id 1. */
+    TEST_ASSERT_FALSE(repl_dispatch(&sim, "delete 1x"));
+    TEST_ASSERT_EQUAL_INT(1, sim.repl_state->nbreakpoints);
+
+    printf("test_delete_non_numeric_id_rejected: PASS\n");
+}
+
 static void test_info_break_lists_breakpoints_with_filters(void)
 {
     xce_sched_sim_driver_t sim;
@@ -1997,6 +2035,7 @@ int main(void)
     RUN_TEST(test_break_malformed_filter_rejected);
     RUN_TEST(test_delete_by_id_removes_one_breakpoint);
     RUN_TEST(test_delete_all_removes_all_breakpoints);
+    RUN_TEST(test_delete_non_numeric_id_rejected);
     RUN_TEST(test_info_break_lists_breakpoints_with_filters);
 
     RUN_TEST(test_event_breakpoint_matches_jobid_filter);