diff --git a/src/betterproto/casing.py b/src/betterproto/casing.py
index f7d0832b..f281cc81 100644
--- a/src/betterproto/casing.py
+++ b/src/betterproto/casing.py
@@ -8,11 +8,11 @@
 
 # Optionally capitalized word.
 # language=PythonRegExp
-WORD = "[A-Z]*[a-z]*[0-9]*"
+WORD = "[A-Z]*([a-z]|[0-9][A-Z]*)*"
 
 # Uppercase word, not followed by lowercase letters.
 # language=PythonRegExp
-WORD_UPPER = "[A-Z]+(?![a-z])[0-9]*"
+WORD_UPPER = "([A-Z]+(?![a-z])[0-9]*)+"
 
 
 def safe_snake_case(value: str) -> str: