diff --git a/CHANGELOG.md b/CHANGELOG.md
index e2fb2846..710c8b8c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,6 +28,7 @@
 * A `select`'s phantom mousedown is no longer treated as an outside click (fixes #744)
 * A re-dispatched layer click now targets the element actually clicked (fixes #771)
 * Guard against undefined `e.data` in the contextmenu handler (fixes #777)
+* `$(...).contextMenu({x, y})` with missing or non-numeric coordinates now falls back to the element-relative position instead of throwing `No selector specified`, and an explicit `{x: 0, y: 0}` is honoured (fixes #812)
 * Clicking on after the menu was destroyed no longer throws with `useModal: false` (fixes #805)
 
 #### Documentation
@@ -35,6 +36,7 @@
 * Documented using custom SVG icons without a gulp build step (fixes #762)
 * Added a dynamic per-row title example to the menu-title demo (fixes #769)
 * The asynchronous create demo now works on right click (fixes #735)
+* Documented that `$(...).contextMenu({x, y})` takes page coordinates (fixes #812)
 
 ### 2.10.2
 
diff --git a/documentation/docs/plugin-commands.md b/documentation/docs/plugin-commands.md
index bf2ac7e5..4477cfc1 100644
--- a/documentation/docs/plugin-commands.md
+++ b/documentation/docs/plugin-commands.md
@@ -42,6 +42,18 @@ $(".some-selector").contextMenu();
 $(".some-selector").contextMenu({x: 123, y: 123});
 ```
 
+`x` and `y` are **page** coordinates, the same space as `event.pageX` / `event.pageY`, so they include the document scroll. They are not viewport coordinates and they are not relative to the trigger element. Coming from a viewport-based source (`event.clientX` / `event.clientY`, `getBoundingClientRect()`, a canvas or map library) add the current scroll offset:
+
+```
+var rect = element.getBoundingClientRect();
+$(".some-selector").contextMenu({
+  x: rect.left + window.scrollX,
+  y: rect.bottom + window.scrollY
+});
+```
+
+When either `x` or `y` is missing or is not a number, which happens when they are read off an event that carries no pointer position such as a keyboard or synthetic one, the menu falls back to `determinePosition` and is positioned relative to the trigger element, just like `$(".some-selector").contextMenu()`.
+
 ## Manually hide a contextMenu
 
 hide the contextMenu of the first element of the selector:
diff --git a/src/jquery.contextMenu.js b/src/jquery.contextMenu.js
index f771df49..61876800 100644
--- a/src/jquery.contextMenu.js
+++ b/src/jquery.contextMenu.js
@@ -220,14 +220,18 @@
             position: function (opt, x, y) {
                 var offset;
                 // determine contextMenu position
-                if (!x && !y) {
-                    opt.determinePosition.call(this, opt.$menu);
-                    return;
-                } else if (x === 'maintain' && y === 'maintain') {
+                if (x === 'maintain' && y === 'maintain') {
                     // x and y must not be changed (after re-show on command click)
                     offset = opt.$menu.position();
+                } else if (!isCoordinate(x) || !isCoordinate(y)) {
+                    // No usable coordinates: no mouse position at all, or only
+                    // one of the two. Note this deliberately tests for real
+                    // numbers instead of truthiness, so an explicit 0 still
+                    // positions the menu at the page origin.
+                    opt.determinePosition.call(this, opt.$menu);
+                    return;
                 } else {
-                    // x and y are given (by mouse event)
+                    // x and y are given (by mouse event), as page coordinates
                     var offsetParentOffset = opt.$menu.offsetParent().offset();
                     offset = {top: y - offsetParentOffset.top, left: x -offsetParentOffset.left};
                 }
@@ -2576,6 +2580,39 @@
             (selector.nodeType === 1 || (typeof selector.jquery !== 'undefined' && typeof selector.length === 'number'));
     }
 
+    // is the given value usable as a page coordinate? Finite numbers are, and
+    // so are numeric strings, which the positioning arithmetic has always
+    // accepted (`{x: el.dataset.x, ...}`). Note 0 is a perfectly valid
+    // coordinate, so this can never be a truthiness check.
+    function isCoordinate(value) {
+        if (typeof value === 'string') {
+            return value.trim() !== '' && isFinite(Number(value));
+        }
+
+        return typeof value === 'number' && isFinite(value);
+    }
+
+    // is the given `$.fn.contextMenu()` argument the {x, y} positioning
+    // overload rather than a menu definition? Decided on key *presence*, not on
+    // the values: an event that carries no pointer position (a keyboard or
+    // synthetic one) yields {x: undefined, y: undefined}, which is still
+    // clearly meant as a position and must not be mistaken for a menu
+    // definition. A menu definition wins whenever the object also carries a
+    // definition-only key, so an options object with an `x`/`y` of its own
+    // keeps being registered as a menu.
+    // See https://github.com/swisnl/jQuery-contextMenu/issues/812
+    function isCoordinateOperation(operation) {
+        if (!operation || typeof operation !== 'object') {
+            return false;
+        }
+
+        if ('items' in operation || 'selector' in operation || 'build' in operation) {
+            return false;
+        }
+
+        return 'x' in operation || 'y' in operation;
+    }
+
     // resolve a caller-supplied "selector-ish" option (`context`, `appendTo`,
     // the element passed to `fromMenu()`, ...) to a jQuery object without ever
     // letting a string be evaluated as HTML. `$(string)` builds a detached DOM
@@ -2613,12 +2650,18 @@
         if (this.length > 0) {  // this is not a build on demand menu
             if (typeof operation === 'undefined') {
                 this.first().trigger('contextmenu');
-            } else if (typeof operation.x !== 'undefined' && typeof operation.y !== 'undefined') {
-                this.first().trigger($.Event('contextmenu', {
-                    pageX: operation.x,
-                    pageY: operation.y,
-                    mouseButton: operation.button
-                }));
+            } else if (isCoordinateOperation(operation)) {
+                var eventProperties = {mouseButton: operation.button};
+                // Only a complete pair of real numbers can position the menu.
+                // Anything else - undefined coordinates from an event without a
+                // pointer position, a half-filled pair - falls back to the
+                // element-relative default position, i.e. what
+                // `$(...).contextMenu()` does, by leaving pageX/pageY unset.
+                if (isCoordinate(operation.x) && isCoordinate(operation.y)) {
+                    eventProperties.pageX = Number(operation.x);
+                    eventProperties.pageY = Number(operation.y);
+                }
+                this.first().trigger($.Event('contextmenu', eventProperties));
             } else if (operation === 'hide') {
                 var $menu = this.first().data('contextMenu') ? this.first().data('contextMenu').$menu : null;
                 if ($menu) {
diff --git a/test/unit/issue-812-xy-overload.test.js b/test/unit/issue-812-xy-overload.test.js
new file mode 100644
index 00000000..f985c77b
--- /dev/null
+++ b/test/unit/issue-812-xy-overload.test.js
@@ -0,0 +1,270 @@
+QUnit.module('issue 812 - $.fn.contextMenu({x, y}) overload', {
+  beforeEach: function() {
+    var $fixture = $('#qunit-fixture');
+    if ($fixture.length === 0) {
+      $('<div id="qunit-fixture">').appendTo('body');
+      $fixture = $('#qunit-fixture');
+    }
+    $fixture.html('<button class="issue-812-trigger">Trigger</button>');
+  },
+  afterEach: function() {
+    $.contextMenu('destroy');
+    var $fixture = $('#qunit-fixture');
+    if ($fixture.length) {
+      $fixture.html('');
+    }
+  }
+});
+
+// Registers a menu on .issue-812-trigger and records how it gets positioned.
+// Returns the recorder so a test can inspect what reached `position` /
+// `determinePosition`.
+function registerIssue812Menu(extraOptions) {
+  var recorder = {
+    positionArgs: [],
+    determinePositionCalls: 0,
+    showCalls: 0
+  };
+
+  $.contextMenu($.extend({
+    selector: '.issue-812-trigger',
+    determinePosition: function($menu) {
+      recorder.determinePositionCalls++;
+      $menu.css({top: 0, left: 0});
+    },
+    events: {
+      show: function() {
+        recorder.showCalls++;
+      }
+    },
+    items: {
+      copy: {name: 'Copy'}
+    }
+  }, extraOptions || {}));
+
+  return {recorder: recorder};
+}
+
+QUnit.test('{x: undefined, y: undefined} does not throw "No selector specified"', function(assert) {
+  // Regression test for https://github.com/swisnl/jQuery-contextMenu/issues/812
+  // pageX/pageY are undefined for keyboard-originated or synthetic events, so
+  // {x: e.pageX, y: e.pageY} legitimately ends up with undefined values. That
+  // used to fall through to the plain-object branch and be treated as a menu
+  // definition, throwing "No selector specified".
+  var menu = registerIssue812Menu();
+
+  var thrown = null;
+  try {
+    $('.issue-812-trigger').contextMenu({x: undefined, y: undefined});
+  } catch (e) {
+    thrown = e;
+  }
+
+  assert.equal(thrown, null, 'showing with undefined coordinates did not throw' + (thrown ? ' (got: ' + thrown.message + ')' : ''));
+  assert.equal(menu.recorder.showCalls, 1, 'the menu was shown');
+  assert.equal(menu.recorder.determinePositionCalls, 1, 'it fell back to the element-relative default position');
+});
+
+QUnit.test('finite coordinates are forwarded as page coordinates', function(assert) {
+  var recorded = [];
+  var menu = registerIssue812Menu({
+    position: function(opt, x, y) {
+      recorded.push([x, y]);
+      opt.$menu.css({top: 0, left: 0});
+    }
+  });
+
+  $('.issue-812-trigger').contextMenu({x: 123, y: 456});
+
+  assert.equal(menu.recorder.showCalls, 1, 'the menu was shown');
+  assert.deepEqual(recorded, [[123, 456]], 'x and y reached position() unchanged');
+});
+
+QUnit.test('numeric strings keep working and arrive as numbers', function(assert) {
+  // The positioning arithmetic has always coped with numeric strings, e.g.
+  // coordinates read straight off a data attribute, so they must not start
+  // silently falling back.
+  var recorded = [];
+  var menu = registerIssue812Menu({
+    position: function(opt, x, y) {
+      recorded.push([x, y]);
+      opt.$menu.css({top: 0, left: 0});
+    }
+  });
+
+  $('.issue-812-trigger').contextMenu({x: '123', y: '456'});
+
+  assert.equal(menu.recorder.determinePositionCalls, 0, 'numeric strings did not fall back');
+  assert.deepEqual(recorded, [[123, 456]], 'numeric strings reached position() as numbers');
+});
+
+QUnit.test('zero is a valid coordinate and is not treated as "no coordinates"', function(assert) {
+  var recorded = [];
+  var menu = registerIssue812Menu({
+    position: function(opt, x, y) {
+      recorded.push([x, y]);
+      opt.$menu.css({top: 0, left: 0});
+    }
+  });
+
+  $('.issue-812-trigger').contextMenu({x: 0, y: 0});
+
+  assert.equal(menu.recorder.showCalls, 1, 'the menu was shown');
+  assert.deepEqual(recorded, [[0, 0]], '0/0 reached position() as real coordinates');
+});
+
+QUnit.test('the default position() places a menu at 0/0 instead of falling back', function(assert) {
+  // The default position() used to bail out to determinePosition() on
+  // `!x && !y`, which also caught the perfectly valid page origin.
+  var menu = registerIssue812Menu();
+
+  $('.issue-812-trigger').contextMenu({x: 0, y: 0});
+
+  assert.equal(menu.recorder.determinePositionCalls, 0, 'determinePosition() was not used for an explicit 0/0');
+});
+
+QUnit.test('a half-filled coordinate pair falls back instead of positioning at NaN', function(assert) {
+  var menu = registerIssue812Menu();
+
+  var thrown = null;
+  try {
+    $('.issue-812-trigger').contextMenu({x: 123, y: undefined});
+  } catch (e) {
+    thrown = e;
+  }
+
+  assert.equal(thrown, null, 'showing with only one coordinate did not throw');
+  assert.equal(menu.recorder.determinePositionCalls, 1, 'it fell back to the element-relative default position');
+
+  var $menu = $('.issue-812-trigger').data('contextMenu').$menu;
+  assert.notOk(isNaN(parseFloat($menu.css('top'))), 'the menu top is a real number');
+  assert.notOk(isNaN(parseFloat($menu.css('left'))), 'the menu left is a real number');
+});
+
+QUnit.test('non-numeric coordinates fall back to the element-relative position', function(assert) {
+  var menu = registerIssue812Menu();
+
+  var thrown = null;
+  try {
+    $('.issue-812-trigger').contextMenu({x: 'nope', y: null});
+  } catch (e) {
+    thrown = e;
+  }
+
+  assert.equal(thrown, null, 'showing with non-numeric coordinates did not throw');
+  assert.equal(menu.recorder.showCalls, 1, 'the menu was shown');
+  assert.equal(menu.recorder.determinePositionCalls, 1, 'it fell back to the element-relative default position');
+});
+
+QUnit.test('an omitted coordinate key falls back as well', function(assert) {
+  // Raised in review: {x: 123} - the key genuinely missing rather than
+  // undefined - must behave the same as {x: 123, y: undefined}.
+  var menu = registerIssue812Menu();
+
+  var thrown = null;
+  try {
+    $('.issue-812-trigger').contextMenu({x: 123});
+  } catch (e) {
+    thrown = e;
+  }
+
+  assert.equal(thrown, null, 'showing with only an x key did not throw');
+  assert.equal(menu.recorder.determinePositionCalls, 1, 'it fell back to the element-relative default position');
+
+  $('.issue-812-trigger').contextMenu('hide');
+  $('.issue-812-trigger').contextMenu({y: 123});
+  assert.equal(menu.recorder.determinePositionCalls, 2, 'the same goes for only a y key');
+});
+
+QUnit.test('negative coordinates are real coordinates', function(assert) {
+  var recorded = [];
+  var menu = registerIssue812Menu({
+    position: function(opt, x, y) {
+      recorded.push([x, y]);
+      opt.$menu.css({top: 0, left: 0});
+    }
+  });
+
+  $('.issue-812-trigger').contextMenu({x: -5, y: -10});
+
+  assert.equal(menu.recorder.determinePositionCalls, 0, 'negative coordinates did not fall back');
+  assert.deepEqual(recorded, [[-5, -10]], 'negative coordinates reached position() unchanged');
+});
+
+QUnit.test('a menu definition carrying x/y keys is still a menu definition', function(assert) {
+  // The overload is detected by key presence, so a definition object that
+  // happens to have x/y properties of its own must not be hijacked into the
+  // positioning branch.
+  var shown = 0;
+
+  $('#qunit-fixture').contextMenu({
+    selector: '.issue-812-trigger',
+    x: 10,
+    y: 20,
+    events: {
+      show: function() {
+        shown++;
+      }
+    },
+    items: {
+      copy: {name: 'Copy'}
+    }
+  });
+
+  $('.issue-812-trigger').trigger($.Event('contextmenu'));
+
+  assert.equal(shown, 1, 'the definition was registered as a menu, not treated as coordinates');
+});
+
+QUnit.test('a plain object without x/y keys is still treated as a menu definition', function(assert) {
+  var shown = 0;
+
+  $('#qunit-fixture').contextMenu({
+    selector: '.issue-812-trigger',
+    events: {
+      show: function() {
+        shown++;
+      }
+    },
+    items: {
+      copy: {name: 'Copy'}
+    }
+  });
+
+  $('.issue-812-trigger').trigger($.Event('contextmenu'));
+
+  assert.equal(shown, 1, 'the jQuery-fn create shorthand still registers a menu');
+});
+
+QUnit.test('every other $.fn.contextMenu() call shape is unchanged', function(assert) {
+  // Pins the operations that share the same dispatch chain as the {x, y}
+  // overload, so widening the coordinate detection cannot break them.
+  var menu = registerIssue812Menu();
+  var $trigger = $('.issue-812-trigger');
+
+  // no argument at all: show, positioned relative to the element
+  $trigger.contextMenu();
+  assert.equal(menu.recorder.showCalls, 1, 'no-argument form shows the menu');
+  assert.equal(menu.recorder.determinePositionCalls, 1, 'no-argument form positions relative to the element');
+
+  // 'hide'
+  $trigger.contextMenu('hide');
+  assert.notOk($trigger.hasClass('context-menu-active'), '"hide" closed the menu');
+
+  // false / true: disable and re-enable the trigger
+  $trigger.contextMenu(false);
+  assert.ok($trigger.hasClass('context-menu-disabled'), 'false disables the trigger');
+  $trigger.trigger($.Event('contextmenu'));
+  assert.equal(menu.recorder.showCalls, 1, 'a disabled trigger does not show the menu');
+
+  $trigger.contextMenu(true);
+  assert.notOk($trigger.hasClass('context-menu-disabled'), 'true re-enables the trigger');
+  $trigger.trigger($.Event('contextmenu'));
+  assert.equal(menu.recorder.showCalls, 2, 'a re-enabled trigger shows the menu again');
+  $trigger.contextMenu('hide');
+
+  // 'destroy'
+  $trigger.contextMenu('destroy');
+  $trigger.trigger($.Event('contextmenu'));
+  assert.equal(menu.recorder.showCalls, 2, '"destroy" unregistered the menu');
+});