diff --git a/tests/test-mrbtree.c b/tests/test-mrbtree.c
index f8c27918..fe3b6cf3 100644
--- a/tests/test-mrbtree.c
+++ b/tests/test-mrbtree.c
@@ -98,6 +98,7 @@ static void test_uint(void)
   for M_EACH(item, tree, UINT_OPLIST) {
       assert (*item == tab2[k] );
       k ++;
+      assert(k <= 2);
     }
   assert(k == 2);
 
@@ -109,6 +110,7 @@ static void test_uint(void)
   for M_EACH(item, tree, UINT_OPLIST) {
       assert (*item == tab3[k] );
       k ++;
+      assert(k <= 3);
     }
   assert(k == 3);
 
diff --git a/tests/test-msnapshot.c b/tests/test-msnapshot.c
index edbc8722..63374501 100644
--- a/tests/test-msnapshot.c
+++ b/tests/test-msnapshot.c
@@ -354,7 +354,9 @@ static void test_double(void)
   double *p = SnapshotDouble_get_write_buffer(s);
   *p = 42.0;
   p = SnapshotDouble_write(s);
+  assert(p != NULL);
   const double *q = SnapshotDouble_read(s);
+  assert(q != NULL);
   assert (*q == 42.0);
   SnapshotDouble_clear(s);
 }
@@ -364,9 +366,12 @@ static void test_doubleSPMC(void)
   SnapshotDoubleSPMC s;
   SnapshotDoubleSPMC_init(s, 1);
   double *p = SnapshotDoubleSPMC_get_write_buffer(s);
+  assert(p != NULL);
   *p = 42.0;
   p = SnapshotDoubleSPMC_write(s);
+  assert(p != NULL);
   const double *q = SnapshotDoubleSPMC_read_start(s);
+  assert(q != NULL);
   assert (*q == 42.0);
   SnapshotDoubleSPMC_read_end(s, q);
   SnapshotDoubleSPMC_clear(s);
@@ -377,9 +382,11 @@ static void test_doubleMPMC(void)
   SnapshotDoubleMPMC s;
   SnapshotDoubleMPMC_init(s, 1, 1);
   double *p = SnapshotDoubleMPMC_write_start(s);
+  assert(p != NULL);
   *p = 42.0;
   SnapshotDoubleMPMC_write_end(s, p);
   const double *q = SnapshotDoubleMPMC_read_start(s);
+  assert(q != NULL);
   assert (*q == 42.0);
   SnapshotDoubleMPMC_read_end(s, q);
   SnapshotDoubleMPMC_clear(s);
diff --git a/tests/test-mtree.c b/tests/test-mtree.c
index 7b1cb0bf..06f54d27 100644
--- a/tests/test-mtree.c
+++ b/tests/test-mtree.c
@@ -467,7 +467,7 @@ static void test_io(void)
   tree_insert_down(root, 1);
   tree_insert_left(it, 3);
   tree_it_t it4 = tree_insert_right(it, 4);
-  root = tree_insert_up(root, -1);
+  tree_insert_up(root, -1);
   tree_insert_up(it, 5);
   tree_insert_child(it4, 6);
   tree_it_t it7 = tree_insert_child(it4, 7);