diff --git a/Zend/zend_API.c b/Zend/zend_API.c
index fa5365b776d..4e3cdc597bf 100644
--- a/Zend/zend_API.c
+++ b/Zend/zend_API.c
@@ -1520,6 +1520,9 @@ ZEND_API zend_result zend_update_class_constant(zend_class_constant *c, const ze
 	zval_ptr_dtor(&c->value);
 	ZVAL_COPY_VALUE(&c->value, &tmp);
 
+	/* may not return SUCCESS in case of an exception,
+	 * should've returned FAILURE in zval_update_constant_ex! */
+	ZEND_ASSERT(!EG(exception));
 	return SUCCESS;
 }
 
diff --git a/Zend/zend_constants.c b/Zend/zend_constants.c
index efdcb905fd7..a18c393be7f 100644
--- a/Zend/zend_constants.c
+++ b/Zend/zend_constants.c
@@ -487,6 +487,9 @@ ZEND_API zval *zend_get_constant_ex(zend_string *cname, zend_class_entry *scope,
 			CONST_PROTECT_RECURSION(c);
 			zend_deprecated_constant(c, c->name);
 			CONST_UNPROTECT_RECURSION(c);
+			if (UNEXPECTED(EG(exception))) {
+				return NULL;
+			}
 		}
 	}
 	return &c->value;
diff --git a/ext/zend_test/tests/gh19720.phpt b/ext/zend_test/tests/gh19720.phpt
new file mode 100644
index 00000000000..627444c4793
--- /dev/null
+++ b/ext/zend_test/tests/gh19720.phpt
@@ -0,0 +1,22 @@
+--TEST--
+GH-19720 (Assertion failure when error handler throws when accessing a deprecated constant)
+--EXTENSIONS--
+zend_test
+--FILE--
+<?php
+class Test {
+    public const MyConst = [ZEND_TEST_DEPRECATED => 42];
+}
+
+set_error_handler(function ($_, $errstr) {
+    throw new Exception($errstr);
+});
+
+try {
+    var_dump(Test::MyConst);
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+Constant ZEND_TEST_DEPRECATED is deprecated