diff --git a/intl/lwbrk/WordBreaker.cpp b/intl/lwbrk/WordBreaker.cpp
index 9538965b3337..edb3a85c2386 100644
--- a/intl/lwbrk/WordBreaker.cpp
+++ b/intl/lwbrk/WordBreaker.cpp
@@ -53,7 +53,7 @@ WordBreaker::GetClass(char16_t c)
 	  if(IS_ASCII(c))  {
 		  if(ASCII_IS_SPACE(c)) {
 			  return kWbClassSpace;
-		  } else if(ASCII_IS_ALPHA(c) || ASCII_IS_DIGIT(c)) {
+		  } else if(ASCII_IS_ALPHA(c) || ASCII_IS_DIGIT(c) || c == '_') {
 			  return kWbClassAlphaLetter;
 		  } else {
 			  return kWbClassPunct;
diff --git a/layout/generic/nsTextFrame.cpp b/layout/generic/nsTextFrame.cpp
index 7e128234743a..70ee0d7ccd34 100644
--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@@ -8117,9 +8117,14 @@ ClusterIterator::IsPunctuation()
   // Return true for all Punctuation categories (Unicode general category P?),
   // and also for Symbol categories (S?) except for Modifier Symbol, which is
   // kept together with any adjacent letter/number. (Bug 1066756)
-  uint8_t cat = unicode::GetGeneralCategory(mFrag->CharAt(mCharIndex));
+  uint32_t ch = mFrag->CharAt(mCharIndex);
+  uint8_t cat = unicode::GetGeneralCategory(ch);
   switch (cat) {
     case HB_UNICODE_GENERAL_CATEGORY_CONNECT_PUNCTUATION: /* Pc */
+      if (ch == '_') {
+        return false;
+      }
+      MOZ_FALLTHROUGH;
     case HB_UNICODE_GENERAL_CATEGORY_DASH_PUNCTUATION:    /* Pd */
     case HB_UNICODE_GENERAL_CATEGORY_CLOSE_PUNCTUATION:   /* Pe */
     case HB_UNICODE_GENERAL_CATEGORY_FINAL_PUNCTUATION:   /* Pf */
diff --git a/layout/generic/test/test_movement_by_words.html b/layout/generic/test/test_movement_by_words.html
index 6586da427bca..9c2418652e6d 100644
--- a/layout/generic/test/test_movement_by_words.html
+++ b/layout/generic/test/test_movement_by_words.html
@@ -130,15 +130,9 @@ function test1() {
   editor.innerHTML = "layout.word_select.stop_at_punctuation";
   sel.collapse(editor.firstChild, 0);
   testRight(editor.firstChild, 7);
-  testRight(editor.firstChild, 12);
   testRight(editor.firstChild, 19);
-  testRight(editor.firstChild, 24);
-  testRight(editor.firstChild, 27);
   testRight(editor.firstChild, 38);
-  testLeft(editor.firstChild, 27);
-  testLeft(editor.firstChild, 24);
   testLeft(editor.firstChild, 19);
-  testLeft(editor.firstChild, 12);
   testLeft(editor.firstChild, 7);
   testLeft(editor.firstChild, 0);
 
@@ -334,15 +328,9 @@ function test2() {
   editor.innerHTML = "layout.word_select.stop_at_punctuation";
   sel.collapse(editor.firstChild, 0);
   testRight(editor.firstChild, 7);
-  testRight(editor.firstChild, 12);
   testRight(editor.firstChild, 19);
-  testRight(editor.firstChild, 24);
-  testRight(editor.firstChild, 27);
   testRight(editor.firstChild, 38);
-  testLeft(editor.firstChild, 27);
-  testLeft(editor.firstChild, 24);
   testLeft(editor.firstChild, 19);
-  testLeft(editor.firstChild, 12);
   testLeft(editor.firstChild, 7);
   testLeft(editor.firstChild, 0);