diff --git a/gdal/frmts/openjpeg/openjpegdataset.cpp b/gdal/frmts/openjpeg/openjpegdataset.cpp
index 269cf39a117b..f7efa1b2d103 100644
--- a/gdal/frmts/openjpeg/openjpegdataset.cpp
+++ b/gdal/frmts/openjpeg/openjpegdataset.cpp
@@ -128,12 +128,13 @@ static OPJ_SIZE_T JP2OpenJPEGDataset_Read(void* pBuffer, OPJ_SIZE_T nBytes,
                                        void *pUserData)
 {
     JP2OpenJPEGFile* psJP2OpenJPEGFile = (JP2OpenJPEGFile* )pUserData;
-    int nRet = static_cast<int>(VSIFReadL(pBuffer, 1, nBytes, psJP2OpenJPEGFile->fp));
+    OPJ_SIZE_T nRet = static_cast<OPJ_SIZE_T>(VSIFReadL(pBuffer, 1, nBytes, psJP2OpenJPEGFile->fp));
 #ifdef DEBUG_IO
-    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Read(%d) = %d", (int)nBytes, nRet);
+    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Read(" CPL_FRMT_GUIB ") = " CPL_FRMT_GUIB,
+             static_cast<GUIntBig>(nBytes), static_cast<GUIntBig>(nRet));
 #endif
     if (nRet == 0)
-        nRet = -1;
+        nRet = static_cast<OPJ_SIZE_T>(-1);
 
     return nRet;
 }
@@ -146,11 +147,12 @@ static OPJ_SIZE_T JP2OpenJPEGDataset_Write(void* pBuffer, OPJ_SIZE_T nBytes,
                                        void *pUserData)
 {
     JP2OpenJPEGFile* psJP2OpenJPEGFile = (JP2OpenJPEGFile* )pUserData;
-    int nRet = static_cast<int>(VSIFWriteL(pBuffer, 1, nBytes, psJP2OpenJPEGFile->fp));
+    OPJ_SIZE_T nRet = static_cast<OPJ_SIZE_T>(VSIFWriteL(pBuffer, 1, nBytes, psJP2OpenJPEGFile->fp));
 #ifdef DEBUG_IO
-    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Write(%d) = %d", (int)nBytes, nRet);
+    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Write(" CPL_FRMT_GUIB ") = " CPL_FRMT_GUIB,
+             static_cast<GUIntBig>(nBytes), static_cast<GUIntBig>(nRet));
 #endif
-    if( static_cast<OPJ_SIZE_T>(nRet) != nBytes )
+    if( nRet != nBytes )
         return static_cast<OPJ_SIZE_T>(-1);
     return nRet;
 }
@@ -163,7 +165,8 @@ static OPJ_BOOL JP2OpenJPEGDataset_Seek(OPJ_OFF_T nBytes, void * pUserData)
 {
     JP2OpenJPEGFile* psJP2OpenJPEGFile = (JP2OpenJPEGFile* )pUserData;
 #ifdef DEBUG_IO
-    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Seek(%d)", (int)nBytes);
+    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Seek(" CPL_FRMT_GUIB ")",
+             static_cast<GUIntBig>(nBytes));
 #endif
     return VSIFSeekL(psJP2OpenJPEGFile->fp, psJP2OpenJPEGFile->nBaseOffset +nBytes,
                      SEEK_SET) == 0;
@@ -179,8 +182,8 @@ static OPJ_OFF_T JP2OpenJPEGDataset_Skip(OPJ_OFF_T nBytes, void * pUserData)
     vsi_l_offset nOffset = VSIFTellL(psJP2OpenJPEGFile->fp);
     nOffset += nBytes;
 #ifdef DEBUG_IO
-    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Skip(%d -> " CPL_FRMT_GUIB ")",
-             (int)nBytes, (GUIntBig)nOffset);
+    CPLDebug("OPENJPEG", "JP2OpenJPEGDataset_Skip(" CPL_FRMT_GUIB " -> " CPL_FRMT_GUIB ")",
+             static_cast<GUIntBig>(nBytes), static_cast<GUIntBig>(nOffset));
 #endif
     VSIFSeekL(psJP2OpenJPEGFile->fp, nOffset, SEEK_SET);
     return nBytes;