diff --git a/fuzzers/cib_file_fuzzer.c b/fuzzers/cib_file_fuzzer.c
index 36adf1b369..1bd1d2b877 100644
--- a/fuzzers/cib_file_fuzzer.c
+++ b/fuzzers/cib_file_fuzzer.c
@@ -1,48 +1,48 @@
 /*
  * Copyright 2024 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 <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 #include <crm_internal.h>
 #include <crm/cib/internal.h>
 
 int
 LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     char *filename = NULL;
     int fd = 0;
 
     // Have at least some data
     if (size < 5) {
-        return 0;
+        return -1; // Do not add input to testing corpus
     }
 
     filename = crm_strdup_printf("%s/libfuzzer.XXXXXX", pcmk__get_tmpdir());
     fd = mkstemp(filename);
     if (fd == -1) {
         free(filename);
         return 0;
     }
     if (write(fd, data, size) < 0) {
         close(fd);
         unlink(filename);
         free(filename);
         return 0;
     }
     close(fd);
 
     cib_file_read_and_verify(filename, NULL, NULL);
 
     unlink(filename);
     free(filename);
 
     return 0;
 }
diff --git a/fuzzers/iso8601_fuzzer.c b/fuzzers/iso8601_fuzzer.c
index 3747c1d878..0e151c6dbd 100644
--- a/fuzzers/iso8601_fuzzer.c
+++ b/fuzzers/iso8601_fuzzer.c
@@ -1,48 +1,46 @@
 /*
  * Copyright 2024 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 <stdint.h>
 #include <stdlib.h>
 #include <stdio.h>
 
 #include <crm/common/util.h>
 #include <crm/common/internal.h>
 
 int
 LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     char *ns = NULL;
     char *result = NULL;
     time_t epoch = 0;
     pcmk__time_hr_t *now = NULL;
     crm_time_period_t *period = NULL;
 
     // Ensure we have enough data.
     if (size < 10) {
-        return 0;
+        return -1; // Do not add input to testing corpus
     }
     ns = pcmk__assert_alloc(1, size + 1);
     memcpy(ns, data, size);
-    ns[size] = '\0';
 
     period = crm_time_parse_period(ns);
     crm_time_free_period(period);
 
     now = pcmk__time_hr_new(ns);
     pcmk__time_hr_free(now);
 
-    epoch = 0;
     now = pcmk__time_hr_now(&epoch);
     result = pcmk__time_format_hr(ns, now);
     pcmk__time_hr_free(now);
     free(result);
 
     free(ns);
     return 0;
 }
diff --git a/fuzzers/strings_fuzzer.c b/fuzzers/strings_fuzzer.c
index 7b99964189..f8dfc8e39f 100644
--- a/fuzzers/strings_fuzzer.c
+++ b/fuzzers/strings_fuzzer.c
@@ -1,40 +1,40 @@
 /*
  * Copyright 2024 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 <stdint.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <strings.h>
 #include <glib.h>
 
 #include <crm/common/options.h>
 #include <crm/common/util.h>
 #include <crm/common/internal.h>
 
 int
 LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     char *ns = NULL;
     guint res = 0U;
 
     if (size < 10) {
-        return 0;
+        return -1; // Do not add input to testing corpus
     }
     ns = pcmk__assert_alloc(1, size + 1);
     memcpy(ns, data, size);
     ns[size] = '\0';
 
     pcmk__numeric_strcasecmp(ns, ns);
     pcmk__trim(ns);
     pcmk_parse_interval_spec(ns, &res);
     crm_get_msec(ns);
 
     free(ns);
     return 0;
 }
diff --git a/fuzzers/utils_fuzzer.c b/fuzzers/utils_fuzzer.c
index 4fafbd79f9..2cb3a5339b 100644
--- a/fuzzers/utils_fuzzer.c
+++ b/fuzzers/utils_fuzzer.c
@@ -1,34 +1,34 @@
 /*
  * Copyright 2024 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 <stdint.h>
 #include <stdlib.h>
 #include <stdio.h>
 
 #include <crm/common/util.h>
 #include <crm/common/internal.h>
 
 int
 LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
     char *ns = NULL;
     guint result = 0U;
 
     if (size < 10) {
-        return 0;
+        return -1; // Do not add input to testing corpus
     }
     ns = pcmk__assert_alloc(1, size + 1);
     memcpy(ns, data, size);
     ns[size] = '\0';
 
     pcmk_parse_interval_spec(ns, &result);
 
     free(ns);
     return 0;
 }