diff --git a/src/cmake/modules/CUnit/src/main.c.in b/src/cmake/modules/CUnit/src/main.c.in
index f1f0a06..2be3165 100644
--- a/src/cmake/modules/CUnit/src/main.c.in
+++ b/src/cmake/modules/CUnit/src/main.c.in
@@ -10,11 +10,19 @@
  * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
  */
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
+#ifndef _WIN32
+#include <sysexits.h>
+#else
+#define EX_USAGE (64)
+#define EX_SOFTWARE (70)
+#endif /* _WIN32 */
+
 #include <CUnit/Basic.h>
 #include <CUnit/Automated.h>
-#include <CUnit/Test.h>
+#include "CUnit/Test.h"
 
 static struct {
     bool print_help;
@@ -36,7 +44,7 @@ static struct {
     "*"
 };
 
-int patmatch(const char *pat, const char *str)
+static int patmatch(const char *pat, const char *str)
 {
     while (*pat) {
         if (*pat == '?') {
@@ -91,14 +99,19 @@ static void help(const char *name)
     printf("  -r FILENAME  results file for automated run\n");
     printf("  -s PATTERN   run only tests in suites matching pattern\n");
     printf("  -t PATTERN   run only test matching pattern\n");
+    printf("\n");
+    printf("Exit codes:\n");
+    printf("  %-2d  Successful termination\n", EXIT_SUCCESS);
+    printf("  %-2d  One or more failing test cases\n", EXIT_FAILURE);
+    printf("  %-2d  Command line usage error\n", EX_USAGE);
+    printf("  %-2d  Internal software error\n", EX_SOFTWARE);
 }
 
-static CU_ErrorCode parse_options(int argc, char *argv[])
+static int parse_options(int argc, char *argv[])
 {
-    CU_ErrorCode err = CUE_SUCCESS;
+    int err = 0;
 
-
-    for (int i = 1; err == CUE_SUCCESS && i < argc; i++) {
+    for (int i = 1; err == 0 && i < argc; i++) {
         switch ((argv[i][0] == '-') ? argv[i][1] : 0) {
             case 'a':
                 opts.automated = true;
@@ -131,8 +144,7 @@ static CU_ErrorCode parse_options(int argc, char *argv[])
                 }
                 /* FALLS THROUGH */
             default:
-                err = (CU_ErrorCode)256;
-                CU_set_error(err); /* Will print as "Undefined Errpr" */
+                err = 1;
                 break;
         }
     }
@@ -140,7 +152,7 @@ static CU_ErrorCode parse_options(int argc, char *argv[])
     return err;
 }
 
-void
+static void
 add_suite(
     const char *suite,
     CU_InitializeFunc pInitFunc,
@@ -158,7 +170,7 @@ add_suite(
 #define ADD_SUITE(suite, init, clean) \
   add_suite(#suite, init, clean)
 
-void
+static void
 add_test(
     const char *suite,
     const char *test,
@@ -181,19 +193,17 @@ add_test(
 
 int main(int argc, char *argv[])
 {
-    CU_ErrorCode err;
+    int ret = EXIT_SUCCESS;
 
-    if ((err = parse_options(argc, argv)) != CUE_SUCCESS) {
+    if (parse_options(argc, argv) != 0) {
         usage(argv[0]);
-        return (int)err;
+        return EX_USAGE;
     } else if (opts.print_help) {
         help(argv[0]);
-        return CUE_SUCCESS;
-    }
-
-    if ((err = CU_initialize_registry()) != CUE_SUCCESS) {
-      fprintf(stderr, "CU_initialize_registry: %s\n", CU_get_error_msg());
-      return (int)err;
+        return ret;
+    } else if (CU_initialize_registry() != CUE_SUCCESS) {
+        fprintf(stderr, "CU_initialize_registry: %s\n", CU_get_error_msg());
+        return EX_SOFTWARE;
     }
 
 /* CMake will expand the macro below to register all suites and tests. */
@@ -220,13 +230,14 @@ int main(int argc, char *argv[])
         CU_basic_run_tests();
     }
 
-    err = CU_get_error();
-    if (err == CUE_SUCCESS) {
-        err = (CU_ErrorCode)(CU_get_number_of_failures() == 0 ? 0 : 256);
+    if (CU_get_error() != CUE_SUCCESS) {
+        ret = EX_SOFTWARE;
+    } else if (CU_get_number_of_failures() != 0) {
+        ret = EXIT_FAILURE;
     }
 
     CU_cleanup_registry();
 
-    return (int)err;
+    return ret;
 }