diff --git a/src/wp-includes/js/wp-emoji-loader.js b/src/wp-includes/js/wp-emoji-loader.js
index fa33179325..ff73a885c9 100644
--- a/src/wp-includes/js/wp-emoji-loader.js
+++ b/src/wp-includes/js/wp-emoji-loader.js
@@ -14,7 +14,7 @@
 		var canvas = document.createElement( 'canvas' ),
 			context = canvas.getContext && canvas.getContext( '2d' ),
 			stringFromCharCode = String.fromCharCode,
-			tonedata, tone, tone2;
+			flag, flag2, tonedata, tone, tone2;
 
 		if ( ! context || ! context.fillText ) {
 			return false;
@@ -40,7 +40,29 @@
 				 * to a larger image (4-5KB data URL).
 				 */
 				context.fillText( stringFromCharCode( 55356, 56806, 55356, 56826 ), 0, 0 );
-				return canvas.toDataURL().length > 3000;
+				if ( canvas.toDataURL().length < 3000 ) {
+					return false;
+				}
+
+				context.clearRect( 0, 0, canvas.width, canvas.height );
+
+				/*
+				 * Test for rainbow flag compatibility. As the rainbow flag was added out of sequence with
+				 * the usual Unicode release cycle, some browsers support it, and some don't, even if their
+				 * Unicode support is up to date.
+				 *
+				 * To test for support, we try to render it, and compare the rendering to how it would look if
+				 * the browser doesn't render it correctly (white flag emoji + rainbow emoji).
+				 */
+				context.fillText( stringFromCharCode( 55356, 57331, 65039, 8205, 55356, 57096 ), 0, 0 );
+				flag = canvas.toDataURL();
+
+				context.clearRect( 0, 0, canvas.width, canvas.height );
+
+				context.fillText( stringFromCharCode( 55356, 57331, 55356, 57096 ), 0, 0 );
+				flag2 = canvas.toDataURL();
+
+				return flag !== flag2;
 			case 'diversity':
 				/*
 				 * This tests if the browser supports the Emoji Diversity specification, by rendering an
diff --git a/src/wp-includes/js/wp-emoji.js b/src/wp-includes/js/wp-emoji.js
index 4156f01b5f..46cddd02be 100644
--- a/src/wp-includes/js/wp-emoji.js
+++ b/src/wp-includes/js/wp-emoji.js
@@ -134,7 +134,7 @@
 		function test( text ) {
 			// Single char. U+20E3 to detect keycaps. U+00A9 "copyright sign" and U+00AE "registered sign" not included.
 			var single = /[\u203C\u2049\u20E3\u2122\u2139\u2194-\u2199\u21A9\u21AA\u2300\u231A\u231B\u2328\u2388\u23CF\u23E9-\u23F3\u23F8-\u23FA\u24C2\u25AA\u25AB\u25B6\u25C0\u25FB-\u25FE\u2600-\u2604\u260E\u2611\u2614\u2615\u2618\u261D\u2620\u2622\u2623\u2626\u262A\u262E\u262F\u2638\u2639\u263A\u2648-\u2653\u2660\u2663\u2665\u2666\u2668\u267B\u267F\u2692\u2693\u2694\u2696\u2697\u2699\u269B\u269C\u26A0\u26A1\u26AA\u26AB\u26B0\u26B1\u26BD\u26BE\u26C4\u26C5\u26C8\u26CE\u26CF\u26D1\u26D3\u26D4\u26E9\u26EA\u26F0-\u26F5\u26F7-\u26FA\u26FD\u2702\u2705\u2708-\u270D\u270F\u2712\u2714\u2716\u271D\u2721\u2728\u2733\u2734\u2744\u2747\u274C\u274E\u2753\u2754\u2755\u2757\u2763\u2764\u2795\u2796\u2797\u27A1\u27B0\u27BF\u2934\u2935\u2B05\u2B06\u2B07\u2B1B\u2B1C\u2B50\u2B55\u3030\u303D\u3297\u3299]/,
-			// Surrogate pair range. Only tests for the second half. 
+			// Surrogate pair range. Only tests for the second half.
 			pair = /[\uDC00-\uDFFF]/;
 
 			if ( text ) {
@@ -180,8 +180,10 @@
 							return false;
 					}
 
-					if ( settings.supports.everythingExceptFlag && ! /^1f1(?:e[6-9a-f]|f[0-9a-f])-1f1(?:e[6-9a-f]|f[0-9a-f])$/.test( icon ) ) {
-
+					if ( settings.supports.everythingExceptFlag &&
+						! /^1f1(?:e[6-9a-f]|f[0-9a-f])-1f1(?:e[6-9a-f]|f[0-9a-f])$/.test( icon ) && // Country flags
+						! /^(1f3f3-fe0f-200d-1f308|1f3f4-200d-2620-fe0f)$/.test( icon )             // Rainbow and pirate flags
+					) {
 						return false;
 					}