diff --git a/CHANGES.rst b/CHANGES.rst
index 1879f11851..85b096e581 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -14,6 +14,11 @@ API changes
 Service fixes and enhancements
 ------------------------------
 
+mast
+^^^^
+
+- Raise an error if non-string values are passed to ``utils.resolve_object``. [#3435]
+
 
 
 Infrastructure, Utility and Other Changes and Additions
diff --git a/astroquery/mast/tests/test_mast.py b/astroquery/mast/tests/test_mast.py
index 8c1f07147f..e57ada5e28 100644
--- a/astroquery/mast/tests/test_mast.py
+++ b/astroquery/mast/tests/test_mast.py
@@ -601,6 +601,10 @@ def test_resolve_object_single(patch_post):
     with pytest.raises(ResolverError, match='Could not resolve "nonexisting" to a sky position.'):
         mast.Mast.resolve_object("nonexisting")
 
+    # Error if object is not a string
+    with pytest.raises(InvalidQueryError, match='All object names must be strings.'):
+        mast.Mast.resolve_object(1)
+
     # Error if single object cannot be resolved with given resolver
     with pytest.raises(ResolverError, match='Could not resolve "Barnard\'s Star" to a sky position using '
                        'resolver "NED".'):
@@ -622,10 +626,6 @@ def test_resolve_object_multi(patch_post):
         assert obj in coord_dict
         assert isinstance(coord_dict[obj], SkyCoord)
 
-    # Warn if one of the objects cannot be resolved
-    with pytest.warns(InputWarning, match='Could not resolve "nonexisting" to a sky position.'):
-        coord_dict = mast.Mast.resolve_object(["M1", "nonexisting"])
-
     # Resolver specified
     coord_dict = mast.Mast.resolve_object(objects, resolver="SIMBAD")
     assert isinstance(coord_dict, dict)
@@ -633,10 +633,6 @@ def test_resolve_object_multi(patch_post):
         assert obj in coord_dict
         assert isinstance(coord_dict[obj], SkyCoord)
 
-    # Warn if one of the objects can't be resolved with given resolver
-    with pytest.warns(InputWarning, match='Could not resolve "TIC 307210830" to a sky position using resolver "NED"'):
-        mast.Mast.resolve_object(objects[:2], resolver="NED")
-
     # Resolve all
     coord_dict = mast.Mast.resolve_object(objects, resolve_all=True)
     assert isinstance(coord_dict, dict)
@@ -646,6 +642,14 @@ def test_resolve_object_multi(patch_post):
         assert isinstance(obj_dict, dict)
         assert isinstance(obj_dict["SIMBAD"], SkyCoord)
 
+    # Warn if one of the objects cannot be resolved
+    with pytest.warns(InputWarning, match='Could not resolve "nonexisting" to a sky position.'):
+        coord_dict = mast.Mast.resolve_object(["M1", "nonexisting"])
+
+    # Warn if one of the objects can't be resolved with given resolver
+    with pytest.warns(InputWarning, match='Could not resolve "TIC 307210830" to a sky position using resolver "NED"'):
+        mast.Mast.resolve_object(objects[:2], resolver="NED")
+
     # Error if none of the objects can be resolved
     warnings.simplefilter("ignore", category=InputWarning)  # ignore warnings
     with pytest.raises(ResolverError, match='Could not resolve any of the given object names to sky positions.'):
diff --git a/astroquery/mast/utils.py b/astroquery/mast/utils.py
index fa3ff17f71..5a18adce46 100644
--- a/astroquery/mast/utils.py
+++ b/astroquery/mast/utils.py
@@ -154,7 +154,7 @@ def resolve_object(objectname, *, resolver=None, resolve_all=False):
 
     Parameters
     ----------
-    objectname : str
+    objectname : str, or iterable of str
         Name(s) of astronomical object(s) to resolve.
     resolver : str, optional
         The resolver to use when resolving a named target into coordinates. Valid options are "SIMBAD" and "NED".
@@ -179,7 +179,18 @@ def resolve_object(objectname, *, resolver=None, resolve_all=False):
         `~astropy.coordinates.SkyCoord` objects with the resolved coordinates.
     """
     # Normalize input
-    object_names = [objectname] if isinstance(objectname, str) else list(objectname)
+    try:
+        # Strings are iterable, so check explicitly
+        if isinstance(objectname, str):
+            raise TypeError
+        object_names = list(objectname)
+    except TypeError:
+        object_names = [objectname]
+
+    # If any items are not strings, raise an error
+    if not all(isinstance(name, str) for name in object_names):
+        raise InvalidQueryError('All object names must be strings.')
+
     single = len(object_names) == 1
 
     is_catalog = False  # Flag to check if object name belongs to a MAST catalog