diff --git a/dse/clib/data/marshal.c b/dse/clib/data/marshal.c
index 29a6ddc..5e2c4df 100644
--- a/dse/clib/data/marshal.c
+++ b/dse/clib/data/marshal.c
@@ -242,31 +242,28 @@ MarshalSignalMap
 MarshalSignalMap* marshal_generate_signalmap(MarshalMapSpec signal,
     MarshalMapSpec source, SimpleSet* ex_signals, bool is_binary)
 {
-    assert(ex_signals);
-
     HashList index_list;
     hashlist_init(&index_list, signal.count);
 
-    for (size_t i = 0; i < signal.count; i++) {
-        for (size_t j = 0; j < source.count; j++) {
+    for (size_t j = 0; j < source.count; j++) {
+        for (size_t i = 0; i < signal.count; i++) {
             if (strcmp(signal.signal[i], source.signal[j]) == 0) {
                 /* If a set is provided, signal mappings are unique. */
                 if (ex_signals) {
                     /* Match. */
                     if (set_contains(ex_signals, signal.signal[i]) == SET_TRUE) {
                         /* Signal already mapped. */
+                        errno = -EINVAL;
                         for (uint32_t i = 0; i < hashlist_length(&index_list);
                             i++) {
                             free(hashlist_at(&index_list, i));
                         }
                         hashlist_destroy(&index_list);
-                        errno = -EINVAL;
                         return NULL;
                     };
                     /* Mark the Signal as mapped */
                     set_add(ex_signals, signal.signal[i]);
                 }
-
                 IndexItem* index = calloc(1, sizeof(IndexItem));
                 index->signal_idx = i;
                 index->source_idx = j;
diff --git a/tests/data/test_marshal.c b/tests/data/test_marshal.c
index 4595da2..e61631c 100644
--- a/tests/data/test_marshal.c
+++ b/tests/data/test_marshal.c
@@ -290,8 +290,8 @@ void test_marshal__signalmap_generate(void** state)
             },
             .expect = {
                 .count = 4,
-                .signal_index = {0, 1, 2, 3},
-                .source_index = {3, 1, 2, 0},
+                .signal_index = {3, 1, 2, 0},
+                .source_index = {0, 1, 2, 3},
             },
         },
         {
@@ -308,8 +308,8 @@ void test_marshal__signalmap_generate(void** state)
             },
             .expect = {
                 .count = 4,
-                .signal_index = {0, 1, 2, 3},
-                .source_index = {0, 2, 1, 3},
+                .signal_index = {0, 2, 1, 3},
+                .source_index = {0, 1, 2, 3},
             },
         },
         {