diff --git a/src/archiver_grp.c b/src/archiver_grp.c
index 36838ab..b4bb8d3 100644
--- a/src/archiver_grp.c
+++ b/src/archiver_grp.c
@@ -24,11 +24,11 @@
  *  This file written by Ryan C. Gordon.
  */
 
-#if (defined PHYSFS_SUPPORTS_GRP)
-
 #define __PHYSICSFS_INTERNAL__
 #include "physfs_internal.h"
 
+#if PHYSFS_SUPPORTS_GRP
+
 static UNPKentry *grpLoadEntries(PHYSFS_Io *io, PHYSFS_uint32 fileCount)
 {
     PHYSFS_uint32 location = 16;  /* sizeof sig. */
diff --git a/src/archiver_hog.c b/src/archiver_hog.c
index 9441cea..d82f5c0 100644
--- a/src/archiver_hog.c
+++ b/src/archiver_hog.c
@@ -29,11 +29,11 @@
  *  Based on grp.c by Ryan C. Gordon.
  */
 
-#if (defined PHYSFS_SUPPORTS_HOG)
-
 #define __PHYSICSFS_INTERNAL__
 #include "physfs_internal.h"
 
+#if PHYSFS_SUPPORTS_HOG
+
 static UNPKentry *hogLoadEntries(PHYSFS_Io *io, PHYSFS_uint32 *_entCount)
 {
     const PHYSFS_uint64 iolen = io->length(io);
diff --git a/src/archiver_iso9660.c b/src/archiver_iso9660.c
index d1e427a..6fe134b 100644
--- a/src/archiver_iso9660.c
+++ b/src/archiver_iso9660.c
@@ -24,11 +24,11 @@
  * - Ambiguities in the standard
  */
 
-#if (defined PHYSFS_SUPPORTS_ISO9660)
-
 #define __PHYSICSFS_INTERNAL__
 #include "physfs_internal.h"
 
+#if PHYSFS_SUPPORTS_ISO9660
+
 #include <time.h>
 
 /* cache files smaller than this completely in memory */
diff --git a/src/archiver_lzma.c b/src/archiver_lzma.c
index 068177b..bff7156 100644
--- a/src/archiver_lzma.c
+++ b/src/archiver_lzma.c
@@ -7,11 +7,11 @@
  *   by Igor Pavlov.
  */
 
-#if (defined PHYSFS_SUPPORTS_7Z)
-
 #define __PHYSICSFS_INTERNAL__
 #include "physfs_internal.h"
 
+#if PHYSFS_SUPPORTS_7Z
+
 #include "lzma/C/7zCrc.h"
 #include "lzma/C/Archive/7z/7zIn.h"
 #include "lzma/C/Archive/7z/7zExtract.h"
diff --git a/src/archiver_mvl.c b/src/archiver_mvl.c
index 2035218..c68e112 100644
--- a/src/archiver_mvl.c
+++ b/src/archiver_mvl.c
@@ -27,11 +27,11 @@
  *  Based on grp.c by Ryan C. Gordon.
  */
 
-#if (defined PHYSFS_SUPPORTS_MVL)
-
 #define __PHYSICSFS_INTERNAL__
 #include "physfs_internal.h"
 
+#if PHYSFS_SUPPORTS_MVL
+
 static UNPKentry *mvlLoadEntries(PHYSFS_Io *io, PHYSFS_uint32 fileCount)
 {
     PHYSFS_uint32 location = 8;  /* sizeof sig. */
diff --git a/src/archiver_qpak.c b/src/archiver_qpak.c
index fdcf850..b1eb1ca 100644
--- a/src/archiver_qpak.c
+++ b/src/archiver_qpak.c
@@ -29,11 +29,11 @@
  *  This file written by Ryan C. Gordon.
  */
 
-#if (defined PHYSFS_SUPPORTS_QPAK)
-
 #define __PHYSICSFS_INTERNAL__
 #include "physfs_internal.h"
 
+#if PHYSFS_SUPPORTS_QPAK
+
 /* !!! FIXME: what is this here for? */
 #if 1  /* Make this case insensitive? */
 #define QPAK_strcmp(x, y) __PHYSFS_stricmpASCII(x, y)
diff --git a/src/archiver_wad.c b/src/archiver_wad.c
index 9951739..8266a22 100644
--- a/src/archiver_wad.c
+++ b/src/archiver_wad.c
@@ -42,11 +42,11 @@
  *  Ryan C. Gordon.
  */
 
-#if (defined PHYSFS_SUPPORTS_WAD)
-
 #define __PHYSICSFS_INTERNAL__
 #include "physfs_internal.h"
 
+#if PHYSFS_SUPPORTS_WAD
+
 static UNPKentry *wadLoadEntries(PHYSFS_Io *io, PHYSFS_uint32 fileCount)
 {
     PHYSFS_uint32 directoryOffset;
diff --git a/src/archiver_zip.c b/src/archiver_zip.c
index 5dceafa..1992e79 100644
--- a/src/archiver_zip.c
+++ b/src/archiver_zip.c
@@ -7,14 +7,14 @@
  *   by Gilles Vollant.
  */
 
-#if (defined PHYSFS_SUPPORTS_ZIP)
+#define __PHYSICSFS_INTERNAL__
+#include "physfs_internal.h"
+
+#if PHYSFS_SUPPORTS_ZIP
 
 #include <errno.h>
 #include <time.h>
 
-#define __PHYSICSFS_INTERNAL__
-#include "physfs_internal.h"
-
 #define USE_MINIZ 1
 #if USE_MINIZ
 #include "physfs_miniz.h"
diff --git a/src/physfs.c b/src/physfs.c
index 6177c05..6fe11ba 100644
--- a/src/physfs.c
+++ b/src/physfs.c
@@ -68,28 +68,28 @@ extern const PHYSFS_Archiver       __PHYSFS_Archiver_ISO9660;
 
 static const PHYSFS_ArchiveInfo *supported_types[] =
 {
-#if (defined PHYSFS_SUPPORTS_ZIP)
+#if PHYSFS_SUPPORTS_ZIP
     &__PHYSFS_ArchiveInfo_ZIP,
 #endif
-#if (defined PHYSFS_SUPPORTS_7Z)
+#if PHYSFS_SUPPORTS_7Z
     &__PHYSFS_ArchiveInfo_LZMA,
 #endif
-#if (defined PHYSFS_SUPPORTS_GRP)
+#if PHYSFS_SUPPORTS_GRP
     &__PHYSFS_ArchiveInfo_GRP,
 #endif
-#if (defined PHYSFS_SUPPORTS_QPAK)
+#if PHYSFS_SUPPORTS_QPAK
     &__PHYSFS_ArchiveInfo_QPAK,
 #endif
-#if (defined PHYSFS_SUPPORTS_HOG)
+#if PHYSFS_SUPPORTS_HOG
     &__PHYSFS_ArchiveInfo_HOG,
 #endif
-#if (defined PHYSFS_SUPPORTS_MVL)
+#if PHYSFS_SUPPORTS_MVL
     &__PHYSFS_ArchiveInfo_MVL,
 #endif
-#if (defined PHYSFS_SUPPORTS_WAD)
+#if PHYSFS_SUPPORTS_WAD
     &__PHYSFS_ArchiveInfo_WAD,
 #endif
-#if (defined PHYSFS_SUPPORTS_ISO9660)
+#if PHYSFS_SUPPORTS_ISO9660
     &__PHYSFS_ArchiveInfo_ISO9660,
 #endif
     NULL
@@ -97,28 +97,28 @@ static const PHYSFS_ArchiveInfo *supported_types[] =
 
 static const PHYSFS_Archiver *archivers[] =
 {
-#if (defined PHYSFS_SUPPORTS_ZIP)
+#if PHYSFS_SUPPORTS_ZIP
     &__PHYSFS_Archiver_ZIP,
 #endif
-#if (defined PHYSFS_SUPPORTS_7Z)
+#if PHYSFS_SUPPORTS_7Z
     &__PHYSFS_Archiver_LZMA,
 #endif
-#if (defined PHYSFS_SUPPORTS_GRP)
+#if PHYSFS_SUPPORTS_GRP
     &__PHYSFS_Archiver_GRP,
 #endif
-#if (defined PHYSFS_SUPPORTS_QPAK)
+#if PHYSFS_SUPPORTS_QPAK
     &__PHYSFS_Archiver_QPAK,
 #endif
-#if (defined PHYSFS_SUPPORTS_HOG)
+#if PHYSFS_SUPPORTS_HOG
     &__PHYSFS_Archiver_HOG,
 #endif
-#if (defined PHYSFS_SUPPORTS_MVL)
+#if PHYSFS_SUPPORTS_MVL
     &__PHYSFS_Archiver_MVL,
 #endif
-#if (defined PHYSFS_SUPPORTS_WAD)
+#if PHYSFS_SUPPORTS_WAD
     &__PHYSFS_Archiver_WAD,
 #endif
-#if (defined PHYSFS_SUPPORTS_ISO9660)
+#if PHYSFS_SUPPORTS_ISO9660
     &__PHYSFS_Archiver_ISO9660,
 #endif
     NULL
diff --git a/src/physfs_internal.h b/src/physfs_internal.h
index f1f18c3..202afae 100644
--- a/src/physfs_internal.h
+++ b/src/physfs_internal.h
@@ -96,6 +96,28 @@ void __PHYSFS_smallFree(void *ptr);
 #define free(x) Do not use free() directly.
 /* !!! FIXME: add alloca check here. */
 
+#ifndef PHYSFS_SUPPORTS_ZIP
+#define PHYSFS_SUPPORTS_ZIP 1
+#endif
+#ifndef PHYSFS_SUPPORTS_7Z
+#define PHYSFS_SUPPORTS_7Z 0
+#endif
+#ifndef PHYSFS_SUPPORTS_GRP
+#define PHYSFS_SUPPORTS_GRP 0
+#endif
+#ifndef PHYSFS_SUPPORTS_HOG
+#define PHYSFS_SUPPORTS_HOG 0
+#endif
+#ifndef PHYSFS_SUPPORTS_MVL
+#define PHYSFS_SUPPORTS_MVL 0
+#endif
+#ifndef PHYSFS_SUPPORTS_WAD
+#define PHYSFS_SUPPORTS_WAD 0
+#endif
+#ifndef PHYSFS_SUPPORTS_ISO9660
+#define PHYSFS_SUPPORTS_ISO9660 0
+#endif
+
 #define DIR_ARCHIVE_DESCRIPTION  "Non-archive, direct filesystem I/O"
 #define GRP_ARCHIVE_DESCRIPTION  "Build engine Groupfile format"
 #define HOG_ARCHIVE_DESCRIPTION  "Descent I/II HOG file format"