This is a backport of upstream fix http://www.sqlite.org/src/ci/c34cf23efb,
which was released in SQLite 3.6.22.
===============================================================================
--- ext/icu/icu.c.orig	2010-07-30 13:40:12.000000000 -0700
+++ ext/icu/icu.c	2010-07-30 13:40:31.000000000 -0700
@@ -459,7 +459,7 @@
     void *pContext;                           /* sqlite3_user_data() context */
     void (*xFunc)(sqlite3_context*,int,sqlite3_value**);
   } scalars[] = {
-    {"regexp",-1, SQLITE_ANY,          0, icuRegexpFunc},
+    {"regexp", 2, SQLITE_ANY,          0, icuRegexpFunc},
 
     {"lower",  1, SQLITE_UTF16,        0, icuCaseFunc16},
     {"lower",  2, SQLITE_UTF16,        0, icuCaseFunc16},