diff --git a/cpp/src/phonenumbers/phonenumbermatcher.cc b/cpp/src/phonenumbers/phonenumbermatcher.cc
index 2d60ceb4d1..60da8fcfed 100644
--- a/cpp/src/phonenumbers/phonenumbermatcher.cc
+++ b/cpp/src/phonenumbers/phonenumbermatcher.cc
@@ -837,6 +837,11 @@ bool PhoneNumberMatcher::AllNumberGroupsAreExactlyPresent(
     candidate_groups.push_back(digit_block);
   }
 
+  // Guard against size_t underflow when candidate_groups is empty.
+  if (candidate_groups.empty()) {
+    return false;
+  }
+
   // Set this to the last group, skipping it if the number has an extension.
   int candidate_number_group_index = static_cast<int>(
       phone_number.has_extension() ? candidate_groups.size() - 2
diff --git a/cpp/src/phonenumbers/phonenumberutil.cc b/cpp/src/phonenumbers/phonenumberutil.cc
index c0c9d09a04..bf245e5b31 100644
--- a/cpp/src/phonenumbers/phonenumberutil.cc
+++ b/cpp/src/phonenumbers/phonenumberutil.cc
@@ -790,9 +790,9 @@ class PhoneNumberRegExpsAndMappings {
             StrCat("(", kDigits, "|", kRfc3966VisualSeparator, ")")),
         alphanum_(StrCat(kValidAlphaInclUppercase, kDigits)),
         rfc3966_domainlabel_(
-            StrCat("[", alphanum_, "]+((\\-)*[", alphanum_, "])*")),
+            StrCat("[", alphanum_, "]+(-+[", alphanum_, "]+)*")),
         rfc3966_toplabel_(StrCat("[", kValidAlphaInclUppercase,
-                                 "]+((\\-)*[", alphanum_, "])*")),
+                                 "]+(-+[", alphanum_, "]+)*")),
         regexp_factory_(new RegExpFactory()),
         regexp_cache_(new RegExpCache(*regexp_factory_.get(), 128)),
         diallable_char_mappings_(),