diff --git a/src/regexp.c b/src/regexp.c
index 30a604b..8362048 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -7998,6 +7998,8 @@
     bt_regengine.expr = expr;
     nfa_regengine.expr = expr;
 #endif
+    // reg_iswordc() uses rex.reg_buf
+    rex.reg_buf = curbuf;
 
     /*
      * First try the NFA engine, unless backtracking was requested.