diff --git a/src/stdlib/pop.rs b/src/stdlib/pop.rs
index a8632c805..bcf3782a8 100644
--- a/src/stdlib/pop.rs
+++ b/src/stdlib/pop.rs
@@ -72,10 +72,19 @@ impl FunctionExpression for PopFn {
     }
 
     fn type_def(&self, state: &state::TypeState) -> TypeDef {
-        self.value
+        let mut typedef = self.value
             .type_def(state)
             .fallible_unless(Kind::array(Collection::any()))
-            .restrict_array()
+            .restrict_array();
+
+        // Remove last element from type definition if array contains just know elements
+        if let Some(col) = typedef.kind_mut().as_array_mut() {
+            if col.unknown_kind().is_undefined() {
+                col.known_mut().pop_last();
+            }
+        }
+
+        typedef
     }
 }
 
@@ -108,7 +117,6 @@ mod tests {
                 Index::from(2) => Kind::integer(),
                 Index::from(3) => Kind::boolean(),
                 Index::from(4) => Kind::float(),
-                Index::from(5) => Kind::bytes(),
             }),
         }
 
@@ -119,9 +127,7 @@ mod tests {
                 Index::from(0) => Kind::integer(),
                 Index::from(1) => Kind::integer(),
                 Index::from(2) => Kind::integer(),
-                Index::from(3) => Kind::integer(),
             }),
         }
-
     ];
 }