diff --git a/lib/parser.js b/lib/parser.js
index 3aba332..d88fa8c 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -184,7 +184,7 @@ function constructAST (tokens) {
 			//... note the aggregator name
 			const aggregator = token.value;
 			token = tokens[++current];
-			if (token.type !== 'paren' && token.value !== '(') {
+			if (token.type !== 'paren' || token.value !== '(') {
 				throw new Error('aggregators must be followed by opening parenthesis');
 			}
 
@@ -230,7 +230,7 @@ function constructAST (tokens) {
 		if (token.type === 'function') {
 			const func = token.value;
 			token = tokens[++current];
-			if (token.type !== 'paren' && token.value !== '(') {
+			if (token.type !== 'paren' || token.value !== '(') {
 				throw new Error('functions must be followed by opening parenthesis');
 			}
 			token = tokens[++current];