diff --git a/libopenjpeg/j2k_lib.c b/libopenjpeg/j2k_lib.c
index a66e31e9..a96df221 100644
--- a/libopenjpeg/j2k_lib.c
+++ b/libopenjpeg/j2k_lib.c
@@ -33,7 +33,7 @@
 #endif /* _WIN32 */
 #include "opj_includes.h"
 
-double opj_clock(void) {
+OPJ_FLOAT64 opj_clock(void) {
 #ifdef _WIN32
 	/* _WIN32: use QueryPerformance (very accurate) */
     LARGE_INTEGER freq , t ;
diff --git a/libopenjpeg/j2k_lib.h b/libopenjpeg/j2k_lib.h
index 5f3406e5..73a14c7d 100644
--- a/libopenjpeg/j2k_lib.h
+++ b/libopenjpeg/j2k_lib.h
@@ -43,7 +43,7 @@ The functions in J2K_LIB.C are internal utilities mainly used for timing.
 Difference in successive opj_clock() calls tells you the elapsed time
 @return Returns time in seconds
 */
-double opj_clock(void);
+OPJ_FLOAT64 opj_clock(void);
 
 /* ----------------------------------------------------------------------- */
 /*@}*/