diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index fa6cc3934..c0726c1b6 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -5614,6 +5614,20 @@ static void test_highlighting() {
     highlight_tests.push_back({{L"$EMPTY_VARIABLE", highlight_role_t::error}});
     highlight_tests.push_back({{L"\"$EMPTY_VARIABLE\"", highlight_role_t::error}});
 
+    highlight_tests.push_back({
+        {L"echo", highlight_role_t::command},
+        {L"\\UFDFD", highlight_role_t::escape},
+        });
+#if WCHAR_T_BITS > 16
+    highlight_tests.push_back({
+        {L"echo", highlight_role_t::command},
+        {L"\\U10FFFF", highlight_role_t::escape},
+        });
+    highlight_tests.push_back({
+        {L"echo", highlight_role_t::command},
+        {L"\\U110000", highlight_role_t::error},
+        });
+#endif
     const auto saved_flags = fish_features();
     mutable_fish_features().set(features_t::ampersand_nobg_in_token, true);
     for (const highlight_component_list_t &components : highlight_tests) {
diff --git a/src/highlight.cpp b/src/highlight.cpp
index 027756236..79f548933 100644
--- a/src/highlight.cpp
+++ b/src/highlight.cpp
@@ -602,6 +602,8 @@ static void color_string_internal(const wcstring &buffstr, highlight_spec_t base
                             case L'U': {
                                 chars = 8;
                                 max_val = WCHAR_MAX;
+                                // Don't exceed the largest Unicode code point - see #1107.
+                                if (0x10FFFF < max_val) max_val = static_cast<wchar_t>(0x10FFFF);
                                 in_pos++;
                                 break;
                             }