diff --git a/loop/doc/structure_db.rst b/loop/doc/structure_db.rst
index 33c307efb0d515034fdb3d6c01098f41c0bda536..631811ed79575c01da39b5dba4b94ad6a54729b2 100644
--- a/loop/doc/structure_db.rst
+++ b/loop/doc/structure_db.rst
@@ -508,7 +508,7 @@ This example illustrates how to create a custom FragDB based on a StructureDB:
     :param c_stem: The C-stem
     :type c_stem:  :class:`ost.mol.ResidueHandle`
     :param frag_size: Number of residues of the fragment
-    :type frag_size:  :class:`float`
+    :type frag_size:  :class:`int`
     :param extra_bins: Whether to extend the search to include fragments from
                        *extra_bins* additional bins surrounding the bin given by
                        the *n_stem* and *c_stem* geometry. If odd, we extend to