diff --git a/mdagent/tools/base_tools/analysis_tools/salt_bridge_tool.py b/mdagent/tools/base_tools/analysis_tools/salt_bridge_tool.py
index 341b0678..8b42ec7a 100644
--- a/mdagent/tools/base_tools/analysis_tools/salt_bridge_tool.py
+++ b/mdagent/tools/base_tools/analysis_tools/salt_bridge_tool.py
@@ -65,7 +65,7 @@ def find_salt_bridges(
             donor_atoms = self.traj.topology.select(f'resname == "{pair[0]}"')
             acceptor_atoms = self.traj.topology.select(f'resname == "{pair[1]}"')
 
-            if not donor_atoms or not acceptor_atoms:
+            if donor_atoms.size == 0 or acceptor_atoms.size == 0:
                 continue
 
             donor_nitrogens = [  # N atoms in the donor residues (e.g. Arg, Lys, His)