diff --git a/packages/boringlang/src/types/type_system.ts b/packages/boringlang/src/types/type_system.ts
index a405b5a..35e224c 100644
--- a/packages/boringlang/src/types/type_system.ts
+++ b/packages/boringlang/src/types/type_system.ts
@@ -89,6 +89,7 @@ class TypeSystem {
             this.result[comparison.right.name] = comparison.left;
             comparison.right = comparison.left;
           }
+          // check
           if (
             comparison.left.typeUsage !== "UnknownTypeUsage" &&
             comparison.right.typeUsage !== "UnknownTypeUsage"
@@ -121,6 +122,13 @@ class TypeSystem {
               comparison.left.arguments[comparison.operation.argNum];
             comparison.right = comparison.left.arguments[comparison.operation.argNum];
           }
+          // check
+          if (
+            argument.typeUsage !== "UnknownTypeUsage" &&
+            comparison.right.typeUsage !== "UnknownTypeUsage"
+          ) {
+            compareTypes(argument, comparison.right);
+          }
         }
         // return type
         if (comparison.operation.operation === "return") {
@@ -145,6 +153,13 @@ class TypeSystem {
             this.result[comparison.right.name] = comparison.left.returnType;
             comparison.right = comparison.left.returnType;
           }
+          // check
+          if (
+            comparison.left.returnType.typeUsage !== "UnknownTypeUsage" &&
+            comparison.right.typeUsage !== "UnknownTypeUsage"
+          ) {
+            compareTypes(comparison.left.returnType, comparison.right);
+          }
         }
         if (
           comparison.left.typeUsage === "UnknownTypeUsage" ||