diff --git a/icu4c/source/i18n/regexcmp.cpp b/icu4c/source/i18n/regexcmp.cpp
index c77181d9ec1..968d08123fd 100644
--- a/icu4c/source/i18n/regexcmp.cpp
+++ b/icu4c/source/i18n/regexcmp.cpp
@@ -1962,6 +1962,7 @@ void   RegexCompile::insertOp(int32_t where) {
             opType == URX_CTR_LOOP     ||
             opType == URX_CTR_LOOP_NG  ||
             opType == URX_JMP_SAV      ||
+            opType == URX_JMP_SAV_X    ||
             opType == URX_RELOC_OPRND)    && opValue > where) {
             // Target location for this opcode is after the insertion point and
             //   needs to be incremented to adjust for the insertion.
diff --git a/icu4c/source/test/testdata/regextst.txt b/icu4c/source/test/testdata/regextst.txt
index 3de486ac549..563fb7f20fc 100644
--- a/icu4c/source/test/testdata/regextst.txt
+++ b/icu4c/source/test/testdata/regextst.txt
@@ -1,4 +1,4 @@
-# Copyright (c) 2001-2010 International Business Machines
+# Copyright (c) 2001-2011 International Business Machines
 # Corporation and others. All Rights Reserved.
 #
 #  file:
@@ -1024,11 +1024,15 @@
 "(?!0{5})(\d{5})(?!-?0{4})(-?\d{4})?"    "<0><1>94040</1><2>-3344</2></0>"
 "(?!0{5})(\d{5})(?!-?0{4})(-?\d{4})?"    "94040-0000"
 "(?!0{5})(\d{5})(?!-?0{4})(-?\d{4})?"    "00000-3344"
+
 #
+#    Bug 8666.  Assertion failure on match, bad operand to JMP_SAV_X opcode.
+#
+"((.??)+|A)*"                     "<0><1><2></2></1></0>AAAAABBBBBCCCCCDDDDEEEEE"
+
 #  Random debugging, Temporary
 #
 #"^(?:a?b?)*$"	                  "a--"
-"^(?:a?b?)*$"	                  "a--"
 
 "This is a string with (?:one |two |three )endings"   "<0>This is a string with two endings</0>"
 "((?:a|b|c)whoop-dee-do) | [jkl]|zed"             "x"