diff --git a/bison.simple b/bison.simple
index 88fad589..22e9944e 100644
--- a/bison.simple
+++ b/bison.simple
@@ -37,13 +37,13 @@
 #else /* not sparc */
 /* This used to test MSDOS, but that is a bad idea
    since that is in the user namespace.  */
-#if defined (_MSDOS_) && !defined (__TURBOC__)
+#if (defined (_MSDOS) || defined (_MSDOS_)) && !defined (__TURBOC__)
 #include <malloc.h>
-#else /* not _MSDOS_, or __TURBOC__ */
+#else /* not MSDOS, or __TURBOC__ */
 #if defined(_AIX)
 #include <malloc.h>
  #pragma alloca
-#else /* not MSDOS, __TURBOC__, or _AIX */
+#else /* not MSDOS, or __TURBOC__, or _AIX */
 #ifdef __hpux
 #ifdef __cplusplus
 extern "C" {
@@ -54,7 +54,7 @@ void *alloca ();
 #endif /* not __cplusplus */
 #endif /* __hpux */
 #endif /* not _AIX */
-#endif /* not _MSDOS_, or __TURBOC__ */
+#endif /* not MSDOS, or __TURBOC__ */
 #endif /* not sparc.  */
 #endif /* not GNU C.  */
 #endif /* alloca not defined.  */
diff --git a/src/bison.s1 b/src/bison.s1
index 88fad589..22e9944e 100644
--- a/src/bison.s1
+++ b/src/bison.s1
@@ -37,13 +37,13 @@
 #else /* not sparc */
 /* This used to test MSDOS, but that is a bad idea
    since that is in the user namespace.  */
-#if defined (_MSDOS_) && !defined (__TURBOC__)
+#if (defined (_MSDOS) || defined (_MSDOS_)) && !defined (__TURBOC__)
 #include <malloc.h>
-#else /* not _MSDOS_, or __TURBOC__ */
+#else /* not MSDOS, or __TURBOC__ */
 #if defined(_AIX)
 #include <malloc.h>
  #pragma alloca
-#else /* not MSDOS, __TURBOC__, or _AIX */
+#else /* not MSDOS, or __TURBOC__, or _AIX */
 #ifdef __hpux
 #ifdef __cplusplus
 extern "C" {
@@ -54,7 +54,7 @@ void *alloca ();
 #endif /* not __cplusplus */
 #endif /* __hpux */
 #endif /* not _AIX */
-#endif /* not _MSDOS_, or __TURBOC__ */
+#endif /* not MSDOS, or __TURBOC__ */
 #endif /* not sparc.  */
 #endif /* not GNU C.  */
 #endif /* alloca not defined.  */
diff --git a/src/bison.simple b/src/bison.simple
index 88fad589..22e9944e 100644
--- a/src/bison.simple
+++ b/src/bison.simple
@@ -37,13 +37,13 @@
 #else /* not sparc */
 /* This used to test MSDOS, but that is a bad idea
    since that is in the user namespace.  */
-#if defined (_MSDOS_) && !defined (__TURBOC__)
+#if (defined (_MSDOS) || defined (_MSDOS_)) && !defined (__TURBOC__)
 #include <malloc.h>
-#else /* not _MSDOS_, or __TURBOC__ */
+#else /* not MSDOS, or __TURBOC__ */
 #if defined(_AIX)
 #include <malloc.h>
  #pragma alloca
-#else /* not MSDOS, __TURBOC__, or _AIX */
+#else /* not MSDOS, or __TURBOC__, or _AIX */
 #ifdef __hpux
 #ifdef __cplusplus
 extern "C" {
@@ -54,7 +54,7 @@ void *alloca ();
 #endif /* not __cplusplus */
 #endif /* __hpux */
 #endif /* not _AIX */
-#endif /* not _MSDOS_, or __TURBOC__ */
+#endif /* not MSDOS, or __TURBOC__ */
 #endif /* not sparc.  */
 #endif /* not GNU C.  */
 #endif /* alloca not defined.  */