diff --git a/lib/common/tests/strings/pcmk__compress_test.c b/lib/common/tests/strings/pcmk__compress_test.c
index 9b19b73731..5e131b768d 100644
--- a/lib/common/tests/strings/pcmk__compress_test.c
+++ b/lib/common/tests/strings/pcmk__compress_test.c
@@ -1,47 +1,60 @@
 /*
  * Copyright 2022 the Pacemaker project contributors
  *
  * The version control history for this file may have further details.
  *
  * This source code is licensed under the GNU Lesser General Public License
  * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
  */
 
 #include <crm_internal.h>
 
 #include <crm/common/unittest_internal.h>
 
+#include "mock_private.h"
+
 #define SIMPLE_DATA "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
 
 const char *SIMPLE_COMPRESSED = "BZh41AY&SYO\x1ai";
 
 static void
 simple_compress(void **state)
 {
     char *result = calloc(1024, sizeof(char));
     unsigned int len;
 
     assert_int_equal(pcmk__compress(SIMPLE_DATA, 40, 0, &result, &len), pcmk_rc_ok);
     assert_memory_equal(result, SIMPLE_COMPRESSED, 13);
 }
 
 static void
 max_too_small(void **state)
 {
     char *result = calloc(1024, sizeof(char));
     unsigned int len;
 
     assert_int_equal(pcmk__compress(SIMPLE_DATA, 40, 10, &result, &len), pcmk_rc_error);
 }
 
+static void
+calloc_fails(void **state) {
+    char *result = calloc(1024, sizeof(char));
+    unsigned int len;
+
+    pcmk__mock_calloc = true;   // calloc() will return NULL
+    pcmk__assert_asserts(pcmk__compress(SIMPLE_DATA, 40, 0, &result, &len));
+    pcmk__mock_calloc = false;  // Use the real calloc()
+}
+
 int
 main(int argc, char **argv)
 {
     const struct CMUnitTest tests[] = {
         cmocka_unit_test(simple_compress),
         cmocka_unit_test(max_too_small),
+        cmocka_unit_test(calloc_fails),
     };
 
     cmocka_set_message_output(CM_OUTPUT_TAP);
     return cmocka_run_group_tests(tests, NULL, NULL);
 }