diff --git a/test/rule-syntax-check.py b/test/rule-syntax-check.py
index 7ee34eb700..a245432b62 100755
--- a/test/rule-syntax-check.py
+++ b/test/rule-syntax-check.py
@@ -34,7 +34,9 @@ args_tests = re.compile(r'(ATTRS?|ENV|TEST){([a-zA-Z0-9/_.*%-]+)}\s*(?:=|!)=\s*'
 no_args_assign = re.compile(r'(NAME|SYMLINK|OWNER|GROUP|MODE|TAG|RUN|LABEL|GOTO|OPTIONS|IMPORT)\s*(?:\+=|:=|=)\s*' + quoted_string_re + '$')
 args_assign = re.compile(r'(ATTR|ENV|IMPORT|RUN){([a-zA-Z0-9/_.*%-]+)}\s*(=|\+=)\s*' + quoted_string_re + '$')
 # Find comma-separated groups, but allow commas that are inside quoted strings.
-comma_separated_group_re = re.compile(r'(?:[^,"]|' + quoted_string_re + ')+')
+# Using quoted_string_re + '?' so that strings missing the last double quote
+# will still match for this part that splits on commas.
+comma_separated_group_re = re.compile(r'(?:[^,"]|' + quoted_string_re + '?)+')
 
 result = 0
 buffer = ''