diff --git a/NEWS b/NEWS
index 2789d02634c..c25c1922f8b 100644
--- a/NEWS
+++ b/NEWS
@@ -54,6 +54,8 @@ PHP                                                                        NEWS
   . Fixed bug GH-19701 (Serialize/deserialize loses some data). (nielsdos)
   . Fixed bug GH-19801 (leaks in var_dump() and debug_zval_dump()).
     (alexandre-daubois)
+  . Fixed bug GH-20043 (array_unique assertion failure with RC1 array
+    causing an exception on sort). (nielsdos)
 
 - Streams:
   . Fixed bug GH-19248 (Use strerror_r instead of strerror in main).
diff --git a/ext/standard/array.c b/ext/standard/array.c
index f0a81b5ba89..b7b5f82d61c 100644
--- a/ext/standard/array.c
+++ b/ext/standard/array.c
@@ -4900,6 +4900,11 @@ PHP_FUNCTION(array_unique)
 	ZVAL_UNDEF(&arTmp[i].b.val);
 	zend_sort((void *) arTmp, i, sizeof(struct bucketindex),
 			(compare_func_t) cmp, (swap_func_t) array_bucketindex_swap);
+
+	if (UNEXPECTED(EG(exception))) {
+		goto out;
+	}
+
 	/* go through the sorted array and delete duplicates from the copy */
 	lastkept = arTmp;
 	for (cmpdata = arTmp + 1; Z_TYPE(cmpdata->b.val) != IS_UNDEF; cmpdata++) {
@@ -4919,6 +4924,8 @@ PHP_FUNCTION(array_unique)
 			}
 		}
 	}
+
+out:
 	pefree(arTmp, GC_FLAGS(Z_ARRVAL_P(array)) & IS_ARRAY_PERSISTENT);
 
 	if (in_place) {
diff --git a/ext/standard/tests/array/gh20043.phpt b/ext/standard/tests/array/gh20043.phpt
new file mode 100644
index 00000000000..d5c7e06417f
--- /dev/null
+++ b/ext/standard/tests/array/gh20043.phpt
@@ -0,0 +1,12 @@
+--TEST--
+GH-20043 (array_unique assertion failure with RC1 array causing an exception on sort)
+--FILE--
+<?php
+try {
+	array_unique([new stdClass, new stdClass], SORT_STRING | SORT_FLAG_CASE);
+} catch (Error $e) {
+	echo $e->getMessage();
+}
+?>
+--EXPECT--
+Object of class stdClass could not be converted to string