diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8dfd17d..09ad0d2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,6 +21,11 @@ IF(APPLE AND NOT MACOSX)
     SET(MACOSX TRUE)
 ENDIF(APPLE AND NOT MACOSX)
 
+# And this might be wrong...
+IF (CMAKE_SYSTEM MATCHES OS2)
+    SET(OS2 TRUE)
+ENDIF (CMAKE_SYSTEM MATCHES OS2)
+
 INCLUDE(CheckIncludeFile)
 INCLUDE(CheckLibraryExists)
 INCLUDE(CheckCSourceCompiles)
@@ -58,7 +63,9 @@ IF(CMAKE_COMPILER_IS_GNUCC)
     " PHYSFS_IS_GCC4)
 
     IF(PHYSFS_IS_GCC4)
-        ADD_DEFINITIONS(-fvisibility=hidden)
+        IF (NOT OS2)  # Not supported on OS/2.
+            ADD_DEFINITIONS(-fvisibility=hidden)
+        ENDIF (NOT OS2)
     ENDIF(PHYSFS_IS_GCC4)
 ENDIF(CMAKE_COMPILER_IS_GNUCC)
 
@@ -163,10 +170,10 @@ IF(UNIX)
     ENDIF(BEOS)
 ENDIF(UNIX)
 
-IF(WINDOWS)
+IF(WINDOWS OR OS2)
     SET(PHYSFS_HAVE_CDROM_SUPPORT TRUE)
     SET(PHYSFS_HAVE_THREAD_SUPPORT TRUE)
-ENDIF(WINDOWS)
+ENDIF(WINDOWS OR OS2)
 
 IF(NOT PHYSFS_HAVE_CDROM_SUPPORT)
     ADD_DEFINITIONS(-DPHYSFS_NO_CDROM_SUPPORT=1)