diff --git a/tests/api/test-get-buffer-data-default.c b/tests/api/test-get-buffer-data-default.c
index 7efb37ac..bb08dff6 100644
--- a/tests/api/test-get-buffer-data-default.c
+++ b/tests/api/test-get-buffer-data-default.c
@@ -141,7 +141,7 @@ static duk_ret_t test_slice(duk_context *ctx, void *udata) {
 	sz = (duk_size_t) 0xdeadbeefUL;
 	p = duk_get_buffer_data_default(ctx, -1, &sz, (void *) 0x12345678UL, (duk_size_t) 0x87654321UL);
 	if (p) {
-		printf("p is not NULL, sz=%ld\n", (long) sz);
+		printf("p is not NULL, sz=%lu\n", (unsigned long) sz);
 		for (i = 0; i < sz; i++) {
 			printf("p[%ld] = 0x%02x\n", (long) i, (unsigned int) p[i]);
 		}
@@ -183,7 +183,7 @@ static duk_ret_t test_uncovered_buffer(duk_context *ctx, void *udata) {
 	sz = (duk_size_t) 0xdeadbeefUL;
 	p = duk_get_buffer_data_default(ctx, -1, &sz, (void *) 0x12345678UL, (duk_size_t) 0x87654321UL);
 	if (p) {
-		printf("p is not NULL, sz=%ld\n", (long) sz);
+		printf("p is not NULL, sz=%lu\n", (unsigned long) sz);
 	} else {
 		printf("p is NULL\n");
 	}
@@ -193,7 +193,7 @@ static duk_ret_t test_uncovered_buffer(duk_context *ctx, void *udata) {
 	sz = (duk_size_t) 0xdeadbeefUL;
 	p = duk_get_buffer_data_default(ctx, -1, &sz, (void *) 0x12345678UL, (duk_size_t) 0x87654321UL);
 	if (p) {
-		printf("p is not NULL, sz=%ld\n", (long) sz);
+		printf("p is not NULL, sz=%lu\n", (unsigned long) sz);
 	} else {
 		printf("p is NULL\n");
 	}
@@ -203,7 +203,7 @@ static duk_ret_t test_uncovered_buffer(duk_context *ctx, void *udata) {
 	sz = (duk_size_t) 0xdeadbeefUL;
 	p = duk_get_buffer_data_default(ctx, -1, &sz, (void *) 0x12345678UL, (duk_size_t) 0x87654321UL);
 	if (p) {
-		printf("p is not NULL, sz=%ld\n", (long) sz);
+		printf("p is not NULL, sz=%lu\n", (unsigned long) sz);
 	} else {
 		printf("p is NULL\n");
 	}
@@ -228,7 +228,7 @@ static duk_ret_t test_invalid_index(duk_context *ctx, void *udata) {
 	sz = (duk_size_t) 0xdeadbeefUL;
 	p = duk_get_buffer_data_default(ctx, -1, &sz, (void *) 0x12345678UL, (duk_size_t) 0x87654321UL);
 	if (p) {
-		printf("p is not NULL, sz=%ld\n", (long) sz);
+		printf("p is not NULL, sz=%lu\n", (unsigned long) sz);
 	} else {
 		printf("p is NULL\n");
 	}
diff --git a/tests/api/test-get-buffer-default.c b/tests/api/test-get-buffer-default.c
index 2df2c9e5..608caf74 100644
--- a/tests/api/test-get-buffer-default.c
+++ b/tests/api/test-get-buffer-default.c
@@ -114,7 +114,7 @@ static duk_ret_t test_invalid_index(duk_context *ctx, void *udata) {
 	sz = (duk_size_t) 0xdeadbeefUL;
 	p = duk_get_buffer_default(ctx, -1, &sz, (void *) 0x12345678UL, (duk_size_t) 0x87654321UL);
 	if (p) {
-		printf("p is not NULL, sz=%ld\n", (long) sz);
+		printf("p is not NULL, sz=%lu\n", (unsigned long) sz);
 	} else {
 		printf("p is NULL\n");
 	}
@@ -142,7 +142,7 @@ static duk_ret_t test_buffer_object(duk_context *ctx, void *udata) {
 	sz = (duk_size_t) 0xdeadbeefUL;
 	p = duk_get_buffer_default(ctx, -1, &sz, (void *) 0x12345678UL, (duk_size_t) 0x87654321UL);
 	if (p) {
-		printf("p is not NULL, sz=%ld\n", (long) sz);
+		printf("p is not NULL, sz=%lu\n", (unsigned long) sz);
 	} else {
 		printf("p is NULL\n");
 	}