diff --git a/+dj/conn.m b/+dj/conn.m
index 52db07b6..b6c4cf10 100644
--- a/+dj/conn.m
+++ b/+dj/conn.m
@@ -32,8 +32,18 @@
 
 
 if isa(CONN, 'dj.Connection') && ~reset
-    assert(nargin==0, ...
-        'connection already instantiated. To reconnect, clear functions')
+    if nargin>0
+        if strcmp(CONN.host,host)
+            warning('DataJoint:Connection:AlreadyInstantiated', sprintf([...
+                'Connection already instantiated.\n' ...
+                'Will use existing connection to "' CONN.host '".\n' ...
+                'To reconnect, set reset to true']));
+        else
+            error('DataJoint:Connection:AlreadyInstantiated', sprintf([...
+                'Connection already instantiated to "' CONN.host '".\n' ...
+                'To reconnect, set reset to true']));
+        end
+    end
 else
     % invoke setupDJ
     % optional environment variables specifying the connection.
diff --git a/+tests/TestConnection.m b/+tests/TestConnection.m
index b52a083d..d57d901b 100644
--- a/+tests/TestConnection.m
+++ b/+tests/TestConnection.m
@@ -9,5 +9,26 @@ function testConnection(testCase)
                 testCase.CONN_INFO.user,...
                 testCase.CONN_INFO.password,'',true).isConnected);
         end
+        function testConnectionExists(testCase)
+            % testConnectionExists tests that will not fail if connection open
+            % to the same host.
+            % Fix https://github.com/datajoint/datajoint-matlab/issues/160
+            st = dbstack;
+            disp(['---------------' st(1).name '---------------']);
+            dj.conn(testCase.CONN_INFO.host, '', '', '', '', true)
+            dj.conn(testCase.CONN_INFO.host, '', '', '', '', true)
+        end
+        function testConnectionDiffHost(testCase)
+            % testConnectionDiffHost tests that will fail if connection open
+            % to a different host.
+            % Fix https://github.com/datajoint/datajoint-matlab/issues/160
+            st = dbstack;
+            disp(['---------------' st(1).name '---------------']);
+            dj.conn(testCase.CONN_INFO.host, '', '', '', '', true)
+            
+            testCase.verifyError(@() dj.conn(...
+                'anything', '', '', '', '', true), ...
+                'DataJoint:Connection:AlreadyInstantiated');
+        end
     end
 end
\ No newline at end of file