diff --git a/src/did/+did/query.m b/src/did/+did/query.m
index 0da67bf..22cde46 100644
--- a/src/did/+did/query.m
+++ b/src/did/+did/query.m
@@ -113,8 +113,13 @@
                 query_struct = did.datastructures.emptystruct('field','operation','param1','param2');
             elseif nargin == 1
                 if isstruct(field)
-                    % check arguments
-                    if ~did.datastructures.eqlen(sort(fieldnames(field)),sort({'field','operation','param1','param2'}))
+                    % Validate fieldnames against the expected set.
+                    % fieldnames() returns a 4x1 cell, so build the
+                    % literal as a column too — did.datastructures.eqlen
+                    % checks shape strictly, and a 1x4 vs 4x1 mismatch
+                    % otherwise rejects every well-formed struct input.
+                    if ~did.datastructures.eqlen(sort(fieldnames(field)), ...
+                            sort({'field';'operation';'param1';'param2'}))
                         error('Field names of search structure do not match expected fields.');
                     end
                     query_struct = field;
diff --git a/tests/+did/+unittest/test_query.m b/tests/+did/+unittest/test_query.m
index c5ee84c..e0a9073 100644
--- a/tests/+did/+unittest/test_query.m
+++ b/tests/+did/+unittest/test_query.m
@@ -40,5 +40,27 @@ function test_or_query(testCase)
             testCase.verifyEqual(q_or.searchstructure.param2(1).operation, 'greaterthan');
             testCase.verifyEqual(q_or.searchstructure.param2(1).param1, 30);
         end
+
+        function test_struct_input_accepted(testCase)
+            % did.query accepts a pre-built searchstructure as a
+            % one-arg input. Regression test for the shape-strict
+            % eqlen check that previously rejected every struct
+            % input because sort(fieldnames(...)) returns a 4x1
+            % cell and the validator compared it against a 1x4
+            % cell literal.
+            ss = struct('field', 'base.name', 'operation', 'exact_string', ...
+                'param1', 'myname', 'param2', '');
+            q = did.query(ss);
+            testCase.verifyEqual(q.searchstructure.field, 'base.name');
+            testCase.verifyEqual(q.searchstructure.operation, 'exact_string');
+            testCase.verifyEqual(q.searchstructure.param1, 'myname');
+        end
+
+        function test_struct_input_rejects_unknown_fields(testCase)
+            % The shape fix must NOT loosen the field-set check.
+            ss = struct('field', 'base.name', 'operation', 'exact_string', ...
+                'param1', 'myname', 'extra', 'X');
+            testCase.verifyError(@() did.query(ss), '');
+        end
     end
 end