diff --git a/tests/test-malgo.c b/tests/test-malgo.c
index 63e05295..44a96c58 100644
--- a/tests/test-malgo.c
+++ b/tests/test-malgo.c
@@ -239,7 +239,7 @@ static void test_list(void)
     assert(list_int_equal_p (l1, l3));
   }
 
-  M_LET( (l1, 4, 28, 29, 31, 34), (l2, 1, 3, 31, 32, 33), (l3, 31), LIST_OPLIST(list_int, M_DEFAULT_OPLIST)) {
+  M_LET( (l1, 4, 28, 29, 31, 34), (l2, 1, 3, 31, 32, 33), (l3, (31)), LIST_OPLIST(list_int, M_DEFAULT_OPLIST)) {
     algo_list_sort_intersect(l1, l2);
     assert(list_int_equal_p (l1, l3));
   }
@@ -618,7 +618,7 @@ static void test_insert(void)
 
 static void test_string_utf8(void)
 {
-  M_LET( (s, "H€llo René Chaînôr¬"), string_t)
+  M_LET( (s, ("H€llo René Chaînôr¬") ), string_t)
     M_LET( (ref, 72, 8364, 108, 108, 111, 32, 82, 101, 110, 233, 32, 67, 104, 97, 238, 110, 244, 114, 172), a, array_uint_t) {
     // Convert the string into an array of unicode.
     ALGO_EXTRACT(a, array_uint_t, s, string_t);
diff --git a/tests/test-mcore.c b/tests/test-mcore.c
index 644eb0da..5b89b8a9 100644
--- a/tests/test-mcore.c
+++ b/tests/test-mcore.c
@@ -248,13 +248,13 @@ static void test_let(void)
     M_LET((zz,z), M_CLASSIC_OPLIST(testobj)) {
       assert( testobj_cmp_ui(zz, 12) == 0);
     }
-    M_LET((zz,42), M_OPEXTEND(M_CLASSIC_OPLIST(testobj), INIT_WITH(testobj_init_set_ui))) {
+    M_LET((zz,(42)), M_OPEXTEND(M_CLASSIC_OPLIST(testobj), INIT_WITH(testobj_init_set_ui))) {
       assert( testobj_cmp_ui(zz, 42) == 0);
     }
     M_LET((zz,z), z2, M_CLASSIC_OPLIST(testobj)) {
       assert( testobj_cmp_ui(zz, 12) == 0);
     }
-    M_LET(z3, (zz,42), M_OPEXTEND(M_CLASSIC_OPLIST(testobj), INIT_WITH(testobj_init_set_ui))) {
+    M_LET(z3, (zz,(42)), M_OPEXTEND(M_CLASSIC_OPLIST(testobj), INIT_WITH(testobj_init_set_ui))) {
       assert( testobj_cmp_ui(zz, 42) == 0);
     }
     b = true;
diff --git a/tests/test-mstring.c b/tests/test-mstring.c
index 96d8bdf4..5c9a6a07 100644
--- a/tests/test-mstring.c
+++ b/tests/test-mstring.c
@@ -728,7 +728,7 @@ static void test_bounded_M_LET(void)
     assert (string16_empty_p(x));
   }
   
-  M_LET( (x,"tree"), BOUNDED_STRING_OPLIST(string16)) {
+  M_LET( (x, ("tree")), BOUNDED_STRING_OPLIST(string16)) {
     assert (string16_equal_str_p(x, "tree"));
   }
 
@@ -753,7 +753,7 @@ static void test_M_LET(void)
     string_set(s2, s1);
     assert(string_equal_p(s1, s2));
   }
-  M_LET((s1,"OK"),string_t) {
+  M_LET((s1,("OK")),string_t) {
     assert(string_equal_str_p(s1, "OK"));
   }
   M_LET((s1,"OK S=%d", 16),string_t) {
@@ -764,10 +764,9 @@ static void test_M_LET(void)
     assert(string_empty_p(s2));
     assert(string_equal_str_p(s3, "42-17"));
   }
-  M_LET( (s1, "Hello"), string_t) {
+  M_LET( (s1, ("Hello")), string_t) {
     assert(string_equal_str_p(s1, "Hello"));
 #if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L)
-    // Initalization with another string is only supported in C11 mode.
     M_LET( (s2, s1), string_t) {
       // In C11 mode, string_equal_p accept also C string
       assert(string_equal_p(s2, "Hello"));