diff --git a/storage/sql.go b/storage/sql.go
index eb19d35..2fd5f97 100644
--- a/storage/sql.go
+++ b/storage/sql.go
@@ -285,7 +285,10 @@ func (s *SQLAdapter) GetContext(ctx context.Context, dest any, filter map[string
 	if len(filter) == 0 {
 		return errors.New("filtering is required when getting a resource")
 	}
-	query, bindings := s.buildQuery(filter)
+	query, bindings, err := s.buildQuery(filter)
+	if err != nil {
+		return err
+	}
 	result := s.dbWithCtx(ctx).Where(query, bindings).Find(dest)
 	if result.RowsAffected == 0 {
 		return ErrNotFound
@@ -301,7 +304,10 @@ func (s *SQLAdapter) UpdateContext(ctx context.Context, item any, filter map[str
 	if len(filter) == 0 {
 		return errors.New("filtering is required when updating a resource")
 	}
-	query, bindings := s.buildQuery(filter)
+	query, bindings, err := s.buildQuery(filter)
+	if err != nil {
+		return err
+	}
 	result := s.dbWithCtx(ctx).Where(query, bindings).Save(item)
 	return result.Error
 }
@@ -314,7 +320,10 @@ func (s *SQLAdapter) DeleteContext(ctx context.Context, item any, filter map[str
 	if len(filter) == 0 {
 		return errors.New("filtering is required when deleting a resource")
 	}
-	query, bindings := s.buildQuery(filter)
+	query, bindings, err := s.buildQuery(filter)
+	if err != nil {
+		return err
+	}
 	result := s.dbWithCtx(ctx).Where(query, bindings).Delete(item)
 	return result.Error
 }
@@ -411,9 +420,15 @@ func (s *SQLAdapter) ListContext(ctx context.Context, dest any, sortKey string,
 	if err != nil {
 		return "", fmt.Errorf("failed to list: %w", err)
 	}
+	var query string
+	var bindings map[string]any
+	if len(filter) > 0 {
+		if query, bindings, err = s.buildQuery(filter); err != nil {
+			return "", err
+		}
+	}
 	return s.executePaginatedQuery(ctx, dest, sortKey, sortDirection, limit, cursor, func(q *gorm.DB) *gorm.DB {
-		if len(filter) > 0 {
-			query, bindings := s.buildQuery(filter)
+		if query != "" {
 			return q.Where(query, bindings)
 		}
 		return q
@@ -473,7 +488,10 @@ func (s *SQLAdapter) CountContext(ctx context.Context, dest any, filter map[stri
 	q := s.dbWithCtx(ctx).Model(dest)
 
 	if len(filter) > 0 {
-		query, bindings := s.buildQuery(filter)
+		query, bindings, err := s.buildQuery(filter)
+		if err != nil {
+			return 0, err
+		}
 		q = q.Where(query, bindings)
 	}
 
@@ -494,11 +512,16 @@ func (s *SQLAdapter) QueryContext(ctx context.Context, dest any, statement strin
 }
 
 
-func (s *SQLAdapter) buildQuery(filter map[string]any) (string, map[string]any) {
+// buildQuery rejects keys that aren't plain column names: keys are written
+// into the SQL as-is, only values are bound.
+func (s *SQLAdapter) buildQuery(filter map[string]any) (string, map[string]any, error) {
 	clauses := []string{}
 	bindings := make(map[string]any)
 
 	for key, value := range filter {
+		if !validColumnName.MatchString(key) {
+			return "", nil, fmt.Errorf("invalid filter key %q: must match [a-zA-Z_][a-zA-Z0-9_]*", key)
+		}
 		if value == nil {
 			// For nil values, use IS NULL instead of = @key
 			clauses = append(clauses, fmt.Sprintf("%s IS NULL", key))
@@ -508,5 +531,5 @@ func (s *SQLAdapter) buildQuery(filter map[string]any) (string, map[string]any)
 			bindings[key] = value
 		}
 	}
-	return strings.Join(clauses, " AND "), bindings
+	return strings.Join(clauses, " AND "), bindings, nil
 }
diff --git a/storage/sql_test.go b/storage/sql_test.go
index d266e2e..141869f 100644
--- a/storage/sql_test.go
+++ b/storage/sql_test.go
@@ -210,6 +210,49 @@ func TestSQLAdapterListRejectsInvalidSortKey(t *testing.T) {
 	}
 }
 
+func TestSQLAdapterRejectsUnsafeFilterKeys(t *testing.T) {
+	_, sql := setupSQLCoverage(t)
+	for _, id := range []string{"a", "b", "c"} {
+		if err := sql.Create(&sqlCoverageItem{Id: id, Name: "orig"}); err != nil {
+			t.Fatalf("Create %s: %v", id, err)
+		}
+	}
+	// Without validation this key closes the filter's parentheses and turns
+	// the WHERE into "(1=1) OR (...)", which matches every row.
+	filter := map[string]any{"1=1) OR (1=1": nil, "name": "orig"}
+
+	var got sqlCoverageItem
+	if err := sql.Get(&got, filter); err == nil {
+		t.Fatal("Get = nil error; want the filter key rejected")
+	}
+	var page []sqlCoverageItem
+	if _, err := sql.List(&page, "id", filter, 10, ""); err == nil {
+		t.Fatal("List = nil error; want the filter key rejected")
+	}
+	if _, err := sql.Count(&[]sqlCoverageItem{}, filter); err == nil {
+		t.Fatal("Count = nil error; want the filter key rejected")
+	}
+	if err := sql.Update(&sqlCoverageItem{Id: "a", Name: "changed"}, filter); err == nil {
+		t.Fatal("Update = nil error; want the filter key rejected")
+	}
+	if err := sql.Delete(&sqlCoverageItem{}, filter); err == nil {
+		t.Fatal("Delete = nil error; want the filter key rejected")
+	}
+
+	var rows []sqlCoverageItem
+	if _, err := sql.List(&rows, "id", nil, 10, ""); err != nil {
+		t.Fatalf("List: %v", err)
+	}
+	if len(rows) != 3 {
+		t.Fatalf("rows = %v; want all 3 left", rows)
+	}
+	for _, row := range rows {
+		if row.Name != "orig" {
+			t.Fatalf("rows = %v; want none changed", rows)
+		}
+	}
+}
+
 func TestSQLAdapterListRejectsInvalidSortDirection(t *testing.T) {
 	_, sql := setupSQLCoverage(t)
 	var page []sqlCoverageItem