diff --git a/libavcodec/opts.c b/libavcodec/opts.c
index 5b643db287..44a213397f 100644
--- a/libavcodec/opts.c
+++ b/libavcodec/opts.c
@@ -11,10 +11,7 @@
  */
 
 #include "avcodec.h"
-
-#ifdef CONFIG_OS2
-#define strcasecmp(s1,s2) stricmp(s1,s2)
-#endif
+#include "os_support.h"
 
 const AVOption avoptions_common[] = {
     AVOPTION_CODEC_FLAG("bit_exact", "use only bit-exact stuff", flags, CODEC_FLAG_BITEXACT, 0),
diff --git a/os_support.h b/libavcodec/os_support.h
similarity index 55%
rename from os_support.h
rename to libavcodec/os_support.h
index 38713f2051..2163381bd4 100644
--- a/os_support.h
+++ b/libavcodec/os_support.h
@@ -2,7 +2,7 @@
 #define _OS_SUPPORT_H
 
 /*
- * miscellaneous OS support macros
+ * miscellaneous OS support macros/function
  *
  * For now:
  * usleep()
@@ -21,8 +21,10 @@
 #endif
 
 #if defined(CONFIG_OS2)
-#  include <stdlib.h>
-#  define usleep(t)    _sleep2((t) / 1000)
+#include <stdlib.h>
+static inline usleep(unsigned int t) { return _sleep2((t) / 1000); }
+static inline float floatf(float x) { return floor(n); }
+static inline int strcasecmp(const char* s1, const char* s2) { return stricmp(s1,s2); }
 #endif
 
 #endif /* _OS_SUPPORT_H */
diff --git a/libavcodec/resample.c b/libavcodec/resample.c
index ba2bb81da2..86bed847c4 100644
--- a/libavcodec/resample.c
+++ b/libavcodec/resample.c
@@ -23,10 +23,7 @@
  */
 
 #include "avcodec.h"
-
-#if defined (CONFIG_OS2)
-#define floorf(n) floor(n)
-#endif
+#include "os_support.h"
 
 typedef struct {
     /* fractional resampling */
diff --git a/libavformat/img.c b/libavformat/img.c
index 980f4f981b..ae229a5bba 100644
--- a/libavformat/img.c
+++ b/libavformat/img.c
@@ -18,7 +18,7 @@
  */
 #include <unistd.h>
 #include "avformat.h"
-#include "../os_support.h"
+#include "os_support.h"
 
 typedef struct {
     int width;