diff --git a/src/rsprocess/assert/rsassert.rs b/src/rsprocess/assert/rsassert.rs
index 560795e..6052a60 100644
--- a/src/rsprocess/assert/rsassert.rs
+++ b/src/rsprocess/assert/rsassert.rs
@@ -85,7 +85,9 @@ impl RSassert<EdgeRelablerInput> {
 	    AssertionTypes::System |
 	    AssertionTypes::Context =>
 		Ok(()),
-	    AssertionTypes::NoType |
+	    AssertionTypes::NoType =>
+		Err(format!("No return type, at least one return statement \
+			     required.")),
 	    AssertionTypes::RangeInteger |
 	    AssertionTypes::RangeSet |
 	    AssertionTypes::RangeNeighbours =>
@@ -197,7 +199,9 @@ impl RSassert<NodeRelablerInput> {
 	    AssertionTypes::System |
 	    AssertionTypes::Context =>
 		Ok(()),
-	    AssertionTypes::NoType |
+	    AssertionTypes::NoType =>
+		Err(format!("No return type, at least one return statement \
+			     required.")),
 	    AssertionTypes::RangeInteger |
 	    AssertionTypes::RangeSet |
 	    AssertionTypes::RangeNeighbours =>