diff --git a/src/applications/search/compiler/PhutilSearchQueryCompiler.php b/src/applications/search/compiler/PhutilSearchQueryCompiler.php
--- a/src/applications/search/compiler/PhutilSearchQueryCompiler.php
+++ b/src/applications/search/compiler/PhutilSearchQueryCompiler.php
@@ -243,34 +243,26 @@
           'Query contains unmatched double quotes.'));
     }
 
-    if ($mode == 'operator') {
-      throw new PhutilSearchQueryCompilerSyntaxException(
-        pht(
-          'Query contains operator ("%s") with no search term.',
-          implode('', $current_operator)));
-    }
+    // If the input query has trailing space, like "a b ", we may exit the
+    // parser without a final token.
+    if ($current_function !== null || $current_operator || $current_token) {
+      $token = array(
+        'operator' => $current_operator,
+        'quoted' => false,
+        'value' => $current_token,
+      );
 
-    $token = array(
-      'operator' => $current_operator,
-      'quoted' => false,
-      'value' => $current_token,
-    );
+      if ($enable_functions) {
+        $token['function'] = $current_function;
+      }
 
-    if ($enable_functions) {
-      $token['function'] = $current_function;
+      $tokens[] = $token;
     }
 
-    $tokens[] = $token;
-
     $results = array();
     foreach ($tokens as $token) {
       $value = implode('', $token['value']);
       $operator_string = implode('', $token['operator']);
-
-      if (!strlen($value)) {
-        continue;
-      }
-
       $is_quoted = $token['quoted'];
 
       switch ($operator_string) {
@@ -304,6 +296,24 @@
               $operator_string));
       }
 
+      if (!strlen($value)) {
+        $require_value = $is_quoted;
+
+        switch ($operator) {
+          default:
+            $require_value = true;
+            break;
+        }
+
+        if ($require_value) {
+          throw new PhutilSearchQueryCompilerSyntaxException(
+            pht(
+              'Query contains a token ("%s") with no search term. Query '.
+              'tokens specify text to search for.',
+              $this->getDisplayToken($token)));
+        }
+      }
+
       $result = array(
         'operator' => $operator,
         'quoted' => $is_quoted,
@@ -371,4 +381,23 @@
     return $open_quote.$value.$close_quote;
   }
 
+  private function getDisplayToken(array $token) {
+    if (isset($token['function'])) {
+      $function = $token['function'].':';
+    } else {
+      $function = '';
+    }
+
+    $operator_string = implode('', $token['operator']);
+
+    $value = implode('', $token['value']);
+
+    $is_quoted = $token['quoted'];
+    if ($is_quoted) {
+      $value = $this->quoteToken($value);
+    }
+
+    return sprintf('%s%s%s', $function, $operator_string, $value);
+  }
+
 }
diff --git a/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php b/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php
--- a/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php
+++ b/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php
@@ -36,6 +36,13 @@
       '"cat' => false,
       'A"' => false,
       'A"B"' => '+"A" +"B"',
+
+      // Trailing whitespace should be discarded.
+      'a b ' => '+"a" +"b"',
+
+      // Functions must have search text.
+      '""' => false,
+      '-' => false,
     );
 
     $this->assertCompileQueries($tests);
@@ -56,7 +63,6 @@
       'cat -dog' => '+[cat] -[dog]',
     );
     $this->assertCompileQueries($quote_tests, '+ -><()~*:[]&|');
-
   }
 
   public function testCompileQueriesWithStemming() {
@@ -133,6 +139,9 @@
       '"'.$mao.'"' => array(
         array(null, $op_and, $mao),
       ),
+      'title:' => false,
+      'title:+' => false,
+      'title:+""' => false,
     );
 
     $this->assertCompileFunctionQueries($function_tests);
@@ -199,15 +208,19 @@
       $compiler = id(new PhutilSearchQueryCompiler())
         ->setEnableFunctions(true);
 
-      $tokens = $compiler->newTokens($input);
+      try {
+        $tokens = $compiler->newTokens($input);
 
-      $result = array();
-      foreach ($tokens as $token) {
-        $result[] = array(
-          $token->getFunction(),
-          $token->getOperator(),
-          $token->getValue(),
-        );
+        $result = array();
+        foreach ($tokens as $token) {
+          $result[] = array(
+            $token->getFunction(),
+            $token->getOperator(),
+            $token->getValue(),
+          );
+        }
+      } catch (PhutilSearchQueryCompilerSyntaxException $ex) {
+        $result = false;
       }
 
       $this->assertEqual(