diff --git a/modulemd/v2/modulemd-module-stream-v1.c b/modulemd/v2/modulemd-module-stream-v1.c
index 4c26f33be..34df203be 100644
--- a/modulemd/v2/modulemd-module-stream-v1.c
+++ b/modulemd/v2/modulemd-module-stream-v1.c
@@ -1075,7 +1075,7 @@ modulemd_module_stream_v1_equals (ModulemdModuleStream *self_1,
   if (v1_self_1->xmd == NULL || v1_self_2->xmd == NULL)
     return FALSE;
 
-  if (g_variant_equal (v1_self_1->xmd, v1_self_2->xmd) != 0)
+  if (!g_variant_equal (v1_self_1->xmd, v1_self_2->xmd))
     return FALSE;
 
   return TRUE;
diff --git a/modulemd/v2/modulemd-module-stream-v2.c b/modulemd/v2/modulemd-module-stream-v2.c
index 24b72a860..ca0beae47 100644
--- a/modulemd/v2/modulemd-module-stream-v2.c
+++ b/modulemd/v2/modulemd-module-stream-v2.c
@@ -231,7 +231,7 @@ modulemd_module_stream_v2_equals (ModulemdModuleStream *self_1,
   if (v2_self_1->xmd == NULL || v2_self_2->xmd == NULL)
     return FALSE;
 
-  if (g_variant_equal (v2_self_1->xmd, v2_self_2->xmd) != 0)
+  if (!g_variant_equal (v2_self_1->xmd, v2_self_2->xmd))
     return FALSE;
 
   return TRUE;
diff --git a/modulemd/v2/modulemd-module.c b/modulemd/v2/modulemd-module.c
index 699e8808a..e6ac372fc 100644
--- a/modulemd/v2/modulemd-module.c
+++ b/modulemd/v2/modulemd-module.c
@@ -329,10 +329,17 @@ modulemd_module_add_stream (ModulemdModule *self,
        * favor of the new one.
        */
 
-      /* TODO: Do a full equality check on the two ModuleStreams once
-       * https://github.com/fedora-modularity/libmodulemd/issues/186 is
-       * fixed.
-       */
+      if (!modulemd_module_stream_equals (old, stream))
+        {
+          /* The two streams have matching NSVCA, but differ in content */
+          g_set_error (error,
+                       MODULEMD_ERROR,
+                       MODULEMD_ERROR_VALIDATE,
+                       "Encountered two streams with matching NSVCA %s but "
+                       "differing content",
+                       modulemd_module_stream_get_NSVCA_as_string (stream));
+          return MD_MODULESTREAM_VERSION_ERROR;
+        }
 
       /* First, drop the existing stream */
       g_ptr_array_remove (self->streams, old);
diff --git a/modulemd/v2/tests/test-modulemd-merger.c b/modulemd/v2/tests/test-modulemd-merger.c
index bac730670..e46b4d844 100644
--- a/modulemd/v2/tests/test-modulemd-merger.c
+++ b/modulemd/v2/tests/test-modulemd-merger.c
@@ -90,8 +90,8 @@ merger_test_deduplicate (CommonMmdTestFixture *fixture,
 
   /* Resolve the merge, which should deduplicate all entries */
   merged_index = modulemd_module_index_merger_resolve (merger, &error);
+  g_assert_no_error (error);
   g_assert_nonnull (merged_index);
-  g_assert_null (error);
 
   deduplicated = modulemd_module_index_dump_to_string (merged_index, &error);
   g_assert_nonnull (deduplicated);