diff --git a/lib/parser.php b/lib/parser.php
index a4fd1164c9378..564a715e4d27e 100644
--- a/lib/parser.php
+++ b/lib/parser.php
@@ -1444,7 +1444,17 @@ public function parse($input) {
 
     if ( ! function_exists( 'ucs2length' ) ) {
         function ucs2length( $string ) {
-            return (int) strlen( iconv( 'UTF-8', 'UTF-16le', $string ) ) / 2;
+    		if ( function_exists( 'iconv' ) ) {
+    			return (int) strlen( iconv( 'UTF-8', 'UTF-16LE', $string ) ) / 2;
+    		}
+
+    		if ( function_exists( 'iconv_fallback' ) ) {
+    			return (int) strlen( iconv_fallback( 'UTF-8', 'UTF16-LE', $string ) );
+    		}
+
+    		// what should we do here?
+    		// this is wrong.
+    		return (int) strlen( $string );
         }
     }
 
diff --git a/packages/block-serialization-default-parser/parser.php b/packages/block-serialization-default-parser/parser.php
index 2e61b178b1c8e..3ec1fa16f81c3 100644
--- a/packages/block-serialization-default-parser/parser.php
+++ b/packages/block-serialization-default-parser/parser.php
@@ -493,6 +493,16 @@ function add_block_from_stack( $end_offset = null ) {
 	}
 
 	static function ucs2length( $string ) {
-		return (int) strlen( iconv( 'UTF-8', 'UTF-16le', $string ) ) / 2;
+		if ( function_exists( 'iconv' ) ) {
+			return (int) strlen( iconv( 'UTF-8', 'UTF-16LE', $string ) ) / 2;
+		}
+
+		if ( function_exists( 'iconv_fallback' ) ) {
+			return (int) strlen( iconv_fallback( 'UTF-8', 'UTF16-LE', $string ) );
+		}
+
+		// what should we do here?
+		// this is wrong.
+		return (int) strlen( $string );
 	}
 }
diff --git a/packages/block-serialization-spec-parser/grammar.pegjs b/packages/block-serialization-spec-parser/grammar.pegjs
index cd75dab727dbd..2796b13e8d043 100644
--- a/packages/block-serialization-spec-parser/grammar.pegjs
+++ b/packages/block-serialization-spec-parser/grammar.pegjs
@@ -52,7 +52,17 @@
 
 if ( ! function_exists( 'ucs2length' ) ) {
     function ucs2length( $string ) {
-        return (int) strlen( iconv( 'UTF-8', 'UTF-16le', $string ) ) / 2;
+		if ( function_exists( 'iconv' ) ) {
+			return (int) strlen( iconv( 'UTF-8', 'UTF-16LE', $string ) ) / 2;
+		}
+
+		if ( function_exists( 'iconv_fallback' ) ) {
+			return (int) strlen( iconv_fallback( 'UTF-8', 'UTF16-LE', $string ) );
+		}
+
+		// what should we do here?
+		// this is wrong.
+		return (int) strlen( $string );
     }
 }
 
diff --git a/packages/block-serialization-spec-parser/index.js b/packages/block-serialization-spec-parser/index.js
index 421877a23f805..05aa1c01c520b 100644
--- a/packages/block-serialization-spec-parser/index.js
+++ b/packages/block-serialization-spec-parser/index.js
@@ -1484,7 +1484,17 @@
 
     if ( ! function_exists( 'ucs2length' ) ) {
         function ucs2length( $string ) {
-            return (int) strlen( iconv( 'UTF-8', 'UTF-16le', $string ) ) / 2;
+    		if ( function_exists( 'iconv' ) ) {
+    			return (int) strlen( iconv( 'UTF-8', 'UTF-16LE', $string ) ) / 2;
+    		}
+
+    		if ( function_exists( 'iconv_fallback' ) ) {
+    			return (int) strlen( iconv_fallback( 'UTF-8', 'UTF16-LE', $string ) );
+    		}
+
+    		// what should we do here?
+    		// this is wrong.
+    		return (int) strlen( $string );
         }
     }