diff --git a/controller/RestController.php b/controller/RestController.php
index 31b1ac114..562a3d2d6 100644
--- a/controller/RestController.php
+++ b/controller/RestController.php
@@ -169,27 +169,30 @@ private function transformSearchResults($request, $results, $parameters)
      * Performs the search function calls. And wraps the result in a json-ld object.
      * @param Request $request
      */
-    public function search($request)
+    public function search(Request $request): void
     {
         $maxhits = $request->getQueryParam('maxhits');
         $offset = $request->getQueryParam('offset');
         $term = $request->getQueryParamRaw('query');
 
-        if (!$term && (!$request->getQueryParam('group') && !$request->getQueryParam('parent'))) {
-            return $this->returnError(400, "Bad Request", "query parameter missing");
+        if ((!isset($term) || strlen(trim($term)) === 0) && (!$request->getQueryParam('group') && !$request->getQueryParam('parent'))) {
+            $this->returnError(400, "Bad Request", "query parameter missing");
+            return;
         }
         if ($maxhits && (!is_numeric($maxhits) || $maxhits <= 0)) {
-            return $this->returnError(400, "Bad Request", "maxhits parameter is invalid");
+            $this->returnError(400, "Bad Request", "maxhits parameter is invalid");
+            return;
         }
         if ($offset && (!is_numeric($offset) || $offset < 0)) {
-            return $this->returnError(400, "Bad Request", "offset parameter is invalid");
+            $this->returnError(400, "Bad Request", "offset parameter is invalid");
+            return;
         }
 
         $parameters = $this->constructSearchParameters($request);
         $results = $this->model->searchConcepts($parameters);
         $ret = $this->transformSearchResults($request, $results, $parameters);
 
-        return $this->returnJson($ret);
+        $this->returnJson($ret);
     }
 
 /** Vocabulary-specific methods **/
diff --git a/tests/RestControllerTest.php b/tests/RestControllerTest.php
index 44f63b300..2bc12d4d8 100644
--- a/tests/RestControllerTest.php
+++ b/tests/RestControllerTest.php
@@ -78,6 +78,41 @@ public function testSearchJsonLdWithAdditionalFields() {
     $this->assertJsonStringEqualsJsonString('{"@context":{"skos":"http:\/\/www.w3.org\/2004\/02\/skos\/core#","isothes":"http:\/\/purl.org\/iso25964\/skos-thes#","onki":"http:\/\/schema.onki.fi\/onki#","uri":"@id","type":"@type","results":{"@id":"onki:results","@container":"@list"},"prefLabel":"skos:prefLabel","altLabel":"skos:altLabel","hiddenLabel":"skos:hiddenLabel","broader":"skos:broader","relatedMatch":"skos:relatedMatch"},"uri":"","results":[{"uri":"http:\/\/www.skosmos.skos\/test\/ta117","type":["skos:Concept","meta:TestClass"],"broader":[{"uri":"http:\/\/www.skosmos.skos\/test\/ta1"}],"relatedMatch":[{"uri":"http:\/\/www.skosmos.skos\/test\/ta115"}],"prefLabel":"3D Bass","lang":"en","vocab":"test"},{"uri":"http:\/\/www.skosmos.skos\/test\/ta116","type":["skos:Concept","meta:TestClass"],"broader":[{"uri":"http:\/\/www.skosmos.skos\/test\/ta1"}],"prefLabel":"Bass","lang":"en","vocab":"test"},{"uri":"http:\/\/www.skosmos.skos\/test\/ta122","type":["skos:Concept","meta:TestClass"],"broader":[{"uri":"http:\/\/www.skosmos.skos\/test\/ta116"}],"prefLabel":"Black sea bass","lang":"en","vocab":"test"}]}', $out);
   }
 
+  /**
+   * Data provider for testSearchWithZero test.
+   */
+  public function testSearchWithZeroData(): array {
+    return [
+      ['0', true],
+      ['1', true],
+      ['-1', true],
+      ['skosmos', true],
+      ['', false],
+      [' ', false]
+    ];
+  }
+
+  /**
+   * @covers RestController::search
+   * @dataProvider testSearchWithZeroData
+   * @param $query string the search query
+   * @param $isSuccess bool whether the request must succeed or fail
+   */
+  public function testSearchWithZero(string $query, bool $isSuccess) {
+    $request = new Request($this->model);
+    $request->setQueryParam('format', 'application/json');
+    $request->setQueryParam('query', $query);
+    $request->setQueryParam('fields', 'broader relatedMatch');
+    $this->controller->search($request);
+
+    $out = $this->getActualOutput();
+    if ($isSuccess) {
+      $this->assertStringNotContainsString("400 Bad Request", $out, "The REST search call returned an unexpected 400 bad request error!");
+    } else {
+      $this->assertStringContainsString("400 Bad Request", $out, "The REST search call DID NOT return an expected 400 bad request error!");
+    }
+  }
+
   /**
    * @covers RestController::indexLetters
    */