diff -ru2 icu/source/i18n/regexcmp.cpp icu/source/i18n/regexcmp.cpp
--- icu/source/i18n/regexcmp.cpp	2013-10-04 22:48:42.000000000 +0200
+++ icu/source/i18n/regexcmp.cpp	2015-04-10 17:59:24.568227804 +0200
@@ -2134,4 +2134,8 @@
             int32_t minML    = minMatchLength(fMatchOpenParen, patEnd);
             int32_t maxML    = maxMatchLength(fMatchOpenParen, patEnd);
+            if (URX_TYPE(maxML) != 0) {
+                error(U_REGEX_LOOK_BEHIND_LIMIT);
+                break;
+            }
             if (maxML == INT32_MAX) {
                 error(U_REGEX_LOOK_BEHIND_LIMIT);
@@ -2167,4 +2171,8 @@
             int32_t minML    = minMatchLength(fMatchOpenParen, patEnd);
             int32_t maxML    = maxMatchLength(fMatchOpenParen, patEnd);
+            if (URX_TYPE(maxML) != 0) {
+                error(U_REGEX_LOOK_BEHIND_LIMIT);
+                break;
+            }
             if (maxML == INT32_MAX) {
                 error(U_REGEX_LOOK_BEHIND_LIMIT);
diff -ru2 icu/source/test/testdata/regextst.txt icu/source/test/testdata/regextst.txt
--- icu/source/test/testdata/regextst.txt	2013-10-04 22:48:12.000000000 +0200
+++ icu/source/test/testdata/regextst.txt	2015-04-10 18:00:41.254717186 +0200
@@ -1174,4 +1174,12 @@
 
 
+# Bug 11370
+#   Max match length computation of look-behind expression gives result that is too big to fit in the
+#   in the 24 bit operand portion of the compiled code. Expressions should fail to compile
+#   (Look-behind match length must be bounded. This case is treated as unbounded, an error.)
+
+"(?<!(0123456789a){10000000})x"         E  "no match"
+"(?<!\\ubeaf(\\ubeaf{11000}){11000})"   E  "no match"
+
 #  Random debugging, Temporary
 #