diff --git a/docs/changelog.rst b/docs/changelog.rst
index b48e608c1..faa3fb33a 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -16,6 +16,8 @@ Released: under development
   for debugging purposes.
   (`#917 <https://github.com/useblocks/sphinx-needs/pull/917>`_)
 
+* Bugfix: Check filter strings for correctness.
+  (`#964 <https://github.com/useblocks/sphinx-needs/pull/964>`_)
 * Bugfix: Replace hardcoded `index` with config value `root_doc`.
   (`#877 <https://github.com/useblocks/sphinx-needs/pull/877>`_)
 * Bugfix: Fix unbounded memory usage in pickle environment.
diff --git a/sphinx_needs/filter_common.py b/sphinx_needs/filter_common.py
index 250bc40aa..a9c6df633 100644
--- a/sphinx_needs/filter_common.py
+++ b/sphinx_needs/filter_common.py
@@ -306,9 +306,14 @@ def filter_single_need(
         # Set filter_context as globals and not only locals in eval()!
         # Otherwise, the vars not be accessed in list comprehensions.
         if filter_compiled:
-            result = bool(eval(filter_compiled, filter_context))
+            result = eval(filter_compiled, filter_context)
         else:
-            result = bool(eval(filter_string, filter_context))
+            result = eval(filter_string, filter_context)
+        if isinstance(result, str):
+            # Raises NeedsInvalidFilter if the result is a string type
+            raise NeedsInvalidFilter(
+                f"Error when evaluating filter: expected output to have True/False but got a string <{result}>"
+            )
     except Exception as e:
         raise NeedsInvalidFilter(f"Filter {filter_string} not valid. Error: {e}.")
-    return result
+    return bool(result)