diff --git a/protogen/names.go b/protogen/names.go
index 445613f..9da11d9 100644
--- a/protogen/names.go
+++ b/protogen/names.go
@@ -136,6 +136,8 @@
 	for ; i < len(s); i++ {
 		c := s[i]
 		switch {
+		case c == '.' && i+1 < len(s) && isASCIILower(s[i+1]):
+			// Skip over .<lowercase>, to match historic behavior.
 		case c == '.':
 			t = append(t, '_') // Convert . to _.
 		case c == '_' && (i == 0 || s[i-1] == '.'):
diff --git a/protogen/names_test.go b/protogen/names_test.go
index 05e698e..3271954 100644
--- a/protogen/names_test.go
+++ b/protogen/names_test.go
@@ -18,8 +18,10 @@
 		{"OneTwo", "OneTwo"},
 		{"_", "X"},
 		{"_a_", "XA_"},
-		{"one.two", "One_Two"},
-		{"one_two.three_four", "OneTwo_ThreeFour"},
+		{"one.two", "OneTwo"},
+		{"one.Two", "One_Two"},
+		{"one_two.three_four", "OneTwoThreeFour"},
+		{"one_two.Three_four", "OneTwo_ThreeFour"},
 		{"_one._two", "XOne_XTwo"},
 		{"SCREAMING_SNAKE_CASE", "SCREAMING_SNAKE_CASE"},
 		{"double__underscore", "Double_Underscore"},