diff --git a/src/cpp-flex.skl b/src/cpp-flex.skl
index 32bedfc8f..2152f7625 100644
--- a/src/cpp-flex.skl
+++ b/src/cpp-flex.skl
@@ -853,6 +853,7 @@ m4_ifdef( [[M4_YY_NOT_IN_HEADER]],
  * corresponding action - sets up yytext.
  */
 #define YY_DO_BEFORE_ACTION \
+	do { \
 	YY_G(yytext_ptr) = yy_bp; \
 	m4_ifdef([[M4_MODE_YYMORE_USED]], [[m4_ifdef([[M4_MODE_NO_YYTEXT_IS_ARRAY]], [[YY_G(yytext_ptr) -= YY_G(yy_more_len); \
 	yyleng = (int) (yy_cp - YY_G(yytext_ptr));]])]]) \
@@ -871,7 +872,8 @@ m4_ifdef([[M4_MODE_YYTEXT_IS_ARRAY]], [[ \
 	m4_ifdef([[M4_MODE_YYMORE_USED]], [[YY_G(yy_more_offset) = 0;]]) \
 	m4_ifdef([[M4_MODE_NO_YYMORE_USED]], [[yy_flex_strncpy( yytext, YY_G(yytext_ptr), yyleng + 1 M4_YY_CALL_LAST_ARG);]]) \
 ]]) \
-	YY_G(yy_c_buf_p) = yy_cp;
+	YY_G(yy_c_buf_p) = yy_cp; \
+	} while(0)
 
 m4_ifdef([[M4_YY_NOT_REENTRANT]], [[
 m4_ifdef( [[M4_MODE_C_ONLY]],