diff --git a/changelog/fragments/991.fixed.rst b/changelog/fragments/991.fixed.rst
new file mode 100644
index 0000000000000000000000000000000000000000..0a6550ffe51c1d6d5592b88875d458784069f6d0
--- /dev/null
+++ b/changelog/fragments/991.fixed.rst
@@ -0,0 +1,2 @@
+An ``MDODiscipline`` now checks the validity of the input data against the grammar before trying to retrieve them
+from the cache.
diff --git a/src/gemseo/utils/comparisons.py b/src/gemseo/utils/comparisons.py
index 432fe63319e70384bda0c59b963aae65da3deb3b..a0e2e7bddd1c827a66b38e21f040b94ea4deca85 100644
--- a/src/gemseo/utils/comparisons.py
+++ b/src/gemseo/utils/comparisons.py
@@ -23,7 +23,9 @@ from collections.abc import Mapping
 from typing import Union
 
 from numpy import asarray
+from numpy import ndarray
 from numpy.linalg import norm
+from scipy.sparse import spmatrix
 from scipy.sparse.linalg import norm as spnorm
 
 from gemseo.utils.compatibility.scipy import ArrayType
@@ -66,6 +68,9 @@ def compare_dict_of_arrays(
     # Check the values
     if tolerance:
         for key, value in dict_of_arrays.items():
+            if not isinstance(value, (ndarray, spmatrix)):
+                return False
+
             difference = other_dict_of_arrays[key] - value
 
             if isinstance(difference, sparse_classes):
@@ -81,6 +86,8 @@ def compare_dict_of_arrays(
                 return False
     else:
         for key, value in dict_of_arrays.items():
+            if not isinstance(value, (ndarray, spmatrix)):
+                return False
             is_different = other_dict_of_arrays[key] != value
 
             if isinstance(is_different, sparse_classes):
diff --git a/tests/core/test_discipline.py b/tests/core/test_discipline.py
index eb775de5d45594e77f66dae6c29ed1d228aa1a2b..ea2dbd1834b52407a38ee6b90b94547d871697e2 100644
--- a/tests/core/test_discipline.py
+++ b/tests/core/test_discipline.py
@@ -1320,3 +1320,27 @@ def test_set_cache_policy_to_none():
     assert isinstance(discipline.cache, SimpleCache)
     discipline.set_cache_policy(discipline.CacheType.NONE)
     assert discipline.cache is None
+
+
+class SimpleDiscipline(MDODiscipline):
+    def __init__(self):
+        super().__init__(grammar_type="JSONGrammar")
+        self.input_grammar.update_from_names(["x"])
+        self.output_grammar.update_from_names(["y"])
+
+    def _run(self):
+        (x,) = self.get_inputs_by_name(["x"])
+        self.local_data["y"] = array([2.0 * x[0]])
+
+
+def test_grammar_same_input_different_types():
+    """Test that a discipline does not return a cached result for invalid data.
+
+    The hash of cached 1d array entry is the same as the hash of the same data as a
+    float, here we test that even if an entry already exists for a numpy array, the
+    cache will not return the cached result if the types are different.
+    """
+    discipline = SimpleDiscipline()
+    discipline.execute({"x": array([1.0])})
+    with pytest.raises(InvalidDataError):
+        discipline.execute({"x": 1.0})