2 files changed, 4 insertions, 1 deletions
diff --git a/sv.h b/sv.h
index 8c98c892cc..a80a0ac083 100644
--- a/sv.h
+++ b/sv.h
@@ -1347,6 +1347,9 @@ the scalar's value cannot change unless written to.
 #  define BmUSEFUL(sv)	((XPVBM*)  SvANY(sv))->xiv_u.xivu_i32
 #  define BmPREVIOUS(sv)	((XPVBM*)  SvANY(sv))->xbm_previous
 #endif
+#define BmPREVIOUS_set(sv, val)						\
+    STMT_START { assert(SvTYPE(sv) == SVt_PVBM);			\
+	(((XPVBM*)SvANY(sv))->xbm_previous = (U16)(val)); } STMT_END
 
 #define FmLINES(sv)	((XPVFM*)  SvANY(sv))->xfm_lines
 
diff --git a/util.c b/util.c
index daf88da933..1ae9459315 100644
--- a/util.c
+++ b/util.c
@@ -522,7 +522,7 @@ Perl_fbm_compile(pTHX_ SV *sv, U32 flags)
 	}
     }
     BmRARE(sv) = s[rarest];
-    BmPREVIOUS(sv) = (U16)rarest;
+    BmPREVIOUS_set(sv, rarest);
     BmUSEFUL(sv) = 100;			/* Initial value */
     if (flags & FBMcf_TAIL)
 	SvTAIL_on(sv);