diff --git a/libtcc.c b/libtcc.c
index 8b942fd5..143dfe92 100644
--- a/libtcc.c
+++ b/libtcc.c
@@ -751,12 +751,15 @@ LIBTCCAPI int tcc_compile_string(TCCState *s, const char *str)
     return tcc_compile(s, s->filetype, str, -1);
 }
 
-/* define a preprocessor symbol. A value can also be provided with the '=' operator */
+/* define a preprocessor symbol. value can be NULL, sym can be "sym=val" */
 LIBTCCAPI void tcc_define_symbol(TCCState *s1, const char *sym, const char *value)
 {
-    if (!value)
-        value = "1";
-    cstr_printf(&s1->cmdline_defs, "#define %s %s\n", sym, value);
+    const char *eq;
+    if (NULL == (eq = strchr(sym, '=')))
+        eq = strchr(sym, 0);
+    if (NULL == value)
+        value = *eq ? eq + 1 : "1";
+    cstr_printf(&s1->cmdline_defs, "#define %.*s %s\n", (int)(eq-sym), sym, value);
 }
 
 /* undefine a preprocessor symbol */
@@ -1713,16 +1716,6 @@ static const FlagDef options_m[] = {
     { 0, 0, NULL }
 };
 
-static void parse_option_D(TCCState *s1, const char *optarg)
-{
-    char *sym = tcc_strdup(optarg);
-    char *value = strchr(sym, '=');
-    if (value)
-        *value++ = '\0';
-    tcc_define_symbol(s1, sym, value);
-    tcc_free(sym);
-}
-
 static void args_parser_add_file(TCCState *s, const char* filename, int filetype)
 {
     struct filespec *f = tcc_malloc(sizeof *f + strlen(filename));
@@ -1863,7 +1856,7 @@ reparse:
             tcc_add_include_path(s, optarg);
             break;
         case TCC_OPTION_D:
-            parse_option_D(s, optarg);
+            tcc_define_symbol(s, optarg, NULL);
             break;
         case TCC_OPTION_U:
             tcc_undefine_symbol(s, optarg);
diff --git a/libtcc.h b/libtcc.h
index e164f5ce..25d247a7 100644
--- a/libtcc.h
+++ b/libtcc.h
@@ -45,7 +45,7 @@ LIBTCCAPI int tcc_add_include_path(TCCState *s, const char *pathname);
 /* add in system include path */
 LIBTCCAPI int tcc_add_sysinclude_path(TCCState *s, const char *pathname);
 
-/* define preprocessor symbol 'sym'. Can put optional value */
+/* define preprocessor symbol 'sym'. value can be NULL, sym can be "sym=val" */
 LIBTCCAPI void tcc_define_symbol(TCCState *s, const char *sym, const char *value);
 
 /* undefine preprocess symbol 'sym' */
diff --git a/tests/libtcc_test_mt.c b/tests/libtcc_test_mt.c
index 2b6cb384..b17e8de2 100644
--- a/tests/libtcc_test_mt.c
+++ b/tests/libtcc_test_mt.c
@@ -104,26 +104,8 @@ void parse_args(TCCState *s)
                 tcc_add_include_path(s, a+2);
             else if (a[1] == 'L')
                 tcc_add_library_path(s, a+2);
-            else if (a[1] == 'D') {
-#if defined(__linux__) \
-  && defined(__STDC_VERSION__) \
-  && (__STDC_VERSION__ >= 201112L)
-                /*
-                 * gcc -std=c11 no longer declare strdup which fails with
-                 * coredump (at least on Linux x64).
-                 */
-                extern char* strdup(const char*);
-#endif
-                char *dup = strdup(a);
-                char *eq = strchr(dup+2, '=');
-                if (eq) {
-                    *eq = 0;
-                    tcc_define_symbol(s, dup+2, eq+1);
-                    *eq = '=';
-                } else
-                  tcc_define_symbol(s, dup+2, NULL);
-                free(dup);
-            }
+            else if (a[1] == 'D')
+                tcc_define_symbol(s, a+2, NULL);
         }
     }
 }
@@ -273,32 +255,32 @@ int main(int argc, char **argv)
     }
 
 #if 1
-    printf("mixed calls\n "), fflush(stdout);
+    printf("running fib with mixed calls\n "), fflush(stdout);
     t = getclock_ms();
     state_test();
-    printf("\n(%u ms)\n", getclock_ms() - t);
+    printf("\n (%u ms)\n", getclock_ms() - t);
 #endif
 #if 1
-    printf("threads\n "), fflush(stdout);
+    printf("running fib in threads\n "), fflush(stdout);
     t = getclock_ms();
     for (n = 0; n < M; ++n)
         create_thread(thread_test_simple, n);
     wait_threads(n);
-    printf("\n(%u ms)\n", getclock_ms() - t);
+    printf("\n (%u ms)\n", getclock_ms() - t);
 #endif
 #if 1
-    printf("tcc in threads\n "), fflush(stdout);
+    printf("running tcc.c in threads to run fib\n"), fflush(stdout);
     t = getclock_ms();
     for (n = 0; n < M; ++n)
         create_thread(thread_test_complex, n);
     wait_threads(n);
-    printf("\n(%u ms)\n", getclock_ms() - t);
+    printf("\n (%u ms)\n", getclock_ms() - t);
 #endif
 #if 1
-    printf("compiling tcc 10 times\n"), fflush(stdout);
+    printf("compiling tcc.c 10 times\n"), fflush(stdout);
     t = getclock_ms();
     time_tcc(10, argv[1]);
-    printf("(%u ms)\n", (getclock_ms() - t) / 10), fflush(stdout);
+    printf(" (%u ms)\n", getclock_ms() - t), fflush(stdout);
 #endif
     return 0;
 }