--- eccodes-2.19.0-Source.unchanged/src/grib_api_prototypes.h	2020-10-15 13:21:34.000000000 +0200
+++ eccodes-2.19.0-Source/src/grib_api_prototypes.h	2020-10-16 08:52:25.171175169 +0200
@@ -859,8 +859,8 @@ double grib_ieeefloat_error(double x);
 double grib_long_to_ieee(unsigned long x);
 int grib_nearest_smaller_ieee_float(double a, double* x);
 unsigned long grib_ieee_to_long(double x);
-unsigned long grib_ieee64_to_long(double x);
-double grib_long_to_ieee64(unsigned long x);
+uint64_t grib_ieee64_to_long(double x);
+double grib_long_to_ieee64(uint64_t x);
 int grib_ieee_decode_array(grib_context* c, unsigned char* buf, size_t nvals, int bytes, double* val);
 int grib_ieee_decode_array(grib_context* c, unsigned char* buf, size_t nvals, int bytes, double* val);
 int grib_ieee_encode_array(grib_context* c, double* val, size_t nvals, int bytes, unsigned char* buf);
--- eccodes-2.19.0-Source.unchanged/src/grib_ieeefloat.c	2020-10-15 13:21:34.000000000 +0200
+++ eccodes-2.19.0-Source/src/grib_ieeefloat.c	2020-10-16 09:01:37.712934707 +0200
@@ -442,7 +442,7 @@ unsigned long grib_ieee_to_long(double x
  * Byte swapping is actually implemented in grib_decode_unsigned_long and
  * grib_encode_unsigned_long.
  */
-unsigned long grib_ieee64_to_long(double x)
+uint64_t grib_ieee64_to_long(double x)
 {
     unsigned long lval;
     DebugAssert(sizeof(double) == sizeof(long));
@@ -450,7 +450,7 @@ unsigned long grib_ieee64_to_long(double
     return lval;
 }
 
-double grib_long_to_ieee64(unsigned long x)
+double grib_long_to_ieee64(uint64_t x)
 {
     double dval;
     DebugAssert(sizeof(double) == sizeof(long));