diff --git a/src/app/core/shared/search/search-configuration.service.spec.ts b/src/app/core/shared/search/search-configuration.service.spec.ts
index d0fbd46d3a2..0b1804a3e6f 100644
--- a/src/app/core/shared/search/search-configuration.service.spec.ts
+++ b/src/app/core/shared/search/search-configuration.service.spec.ts
@@ -20,7 +20,8 @@ describe('SearchConfigurationService', () => {
   const prefixFilter = {
     'f.author': ['another value'],
     'f.date.min': ['2013'],
-    'f.date.max': ['2018']
+    'f.date.max': ['2018'],
+    'f.subject': ['some subject,contains']
   };
   const defaults = new PaginatedSearchOptions({
     pagination: Object.assign(new PaginationComponentOptions(), { id: 'page-id', currentPage: 1, pageSize: 20 }),
@@ -31,8 +32,10 @@ describe('SearchConfigurationService', () => {
   });
 
   const backendFilters = [
-    new SearchFilter('f.author', ['another value']),
-    new SearchFilter('f.date', ['[2013 TO 2018]'], 'equals')
+    new SearchFilter('f.author', ['another value'], 'equals'),
+    new SearchFilter('f.date', ['[2013 TO 2018]'], 'equals'),
+    // value already carries an operator suffix -> operator must stay unset (not overridden to equals)
+    new SearchFilter('f.subject', ['some subject,contains'])
   ];
 
   const routeService = jasmine.createSpyObj('RouteService', {
diff --git a/src/app/core/shared/search/search-configuration.service.ts b/src/app/core/shared/search/search-configuration.service.ts
index eed93ae201c..8f91e1b4977 100644
--- a/src/app/core/shared/search/search-configuration.service.ts
+++ b/src/app/core/shared/search/search-configuration.service.ts
@@ -196,7 +196,15 @@ export class SearchConfigurationService implements OnDestroy {
               filters.push(new SearchFilter(realKey, ['[' + min + ' TO ' + max + ']'], 'equals'));
             }
           } else {
-            filters.push(new SearchFilter(key, filterParams[key]));
+            // Default to the "equals" operator only when a filter value carries none (e.g. a legacy
+            // or crawled URL like "f.subject=foo" instead of "f.subject=foo,equals"), which the
+            // backend would otherwise reject with HTTP 422. Values that already embed an operator
+            // (contain a comma, e.g. "foo,contains") keep it and leave SearchFilter.operator unset,
+            // matching SearchOptions.toRestUrl and consumers that read filter.operator directly
+            // (e.g. CSV export). dspace-customers#781.
+            const values = filterParams[key];
+            const operator = values.every((value) => value.includes(',')) ? undefined : 'equals';
+            filters.push(new SearchFilter(key, values, operator));
           }
         });
         return filters;
diff --git a/src/app/my-dspace-page/my-dspace-configuration.service.spec.ts b/src/app/my-dspace-page/my-dspace-configuration.service.spec.ts
index c388d2d3561..fcbb46c5912 100644
--- a/src/app/my-dspace-page/my-dspace-configuration.service.spec.ts
+++ b/src/app/my-dspace-page/my-dspace-configuration.service.spec.ts
@@ -30,7 +30,7 @@ describe('MyDSpaceConfigurationService', () => {
   });
 
   const backendFilters = [
-    new SearchFilter('f.namedresourcetype', ['another value']),
+    new SearchFilter('f.namedresourcetype', ['another value'], 'equals'),
     new SearchFilter('f.dateSubmitted', ['[2013 TO 2018]'], 'equals')
   ];