diff --git a/ccid/src/ccid.c b/ccid/src/ccid.c
index 3ba9a11..3d1e6e5 100644
--- a/ccid/src/ccid.c
+++ b/ccid/src/ccid.c
@@ -25,6 +25,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "ccid.h"
 #include "sslutil.h"
@@ -191,7 +192,7 @@ static int get_rapdu(sc_apdu_t *apdu, __u8 **buf, size_t *resplen)
         goto err;
     }
 
-    if (apdu->sw1 > 0xff || apdu->sw2 > 0xff || apdu->sw1 < 0 || apdu->sw2 < 0) {
+    if (apdu->sw1 > 0xff || apdu->sw2 > 0xff) {
         sc_debug(ctx, SC_LOG_DEBUG_VERBOSE, "Received invalid status bytes SW1=%d SW2=%d", apdu->sw1, apdu->sw2);
         sc_result = SC_ERROR_INVALID_DATA;
         goto err;
diff --git a/pcsc-relay/src/lnfc.c b/pcsc-relay/src/lnfc.c
index 58d8097..7c0d818 100644
--- a/pcsc-relay/src/lnfc.c
+++ b/pcsc-relay/src/lnfc.c
@@ -223,7 +223,7 @@ static int lnfc_send_rapdu(driver_data_t *driver_data,
         return 0;
     }
     if (r < len)
-        INFO ("Transmitted %d less bytes than desired: %s\n", len-r, nfc_strerror(data->pndTarget));
+        INFO ("Transmitted %u less bytes than desired: %s\n", (unsigned int) len-r, nfc_strerror(data->pndTarget));
 
 
     return 1;
diff --git a/pcsc-relay/src/opicc.c b/pcsc-relay/src/opicc.c
index 8a3da56..0c2ec91 100644
--- a/pcsc-relay/src/opicc.c
+++ b/pcsc-relay/src/opicc.c
@@ -61,7 +61,7 @@ int picc_encode_rapdu(const unsigned char *inbuf, size_t inlen,
     *outlen = length;
 
     /* write length of R-APDU */
-    sprintf(p, "%04X:", inlen);
+    sprintf(p, "%0lX:", inlen);
 
     /* next points to the next byte to encode */
     next = inbuf;
@@ -80,7 +80,8 @@ int picc_decode_apdu(const char *inbuf, size_t inlen,
         unsigned char **outbuf, size_t *outlen)
 {
     size_t pos, length;
-    char *end, *p;
+    char *end;
+    unsigned char *p;
     unsigned long int b;
 
     if (!outbuf || !outlen) {
@@ -219,7 +220,7 @@ static int picc_receive_capdu(driver_data_t *driver_data,
     if (fflush(data->fd) != 0)
         RELAY_ERROR("Warning, fflush failed: %s\n", strerror(errno));
 
-    DEBUG(data->line);
+    DEBUG("%s", data->line);
 
 
     /* decode C-APDU */
diff --git a/pcsc-relay/src/pcsc-relay.c b/pcsc-relay/src/pcsc-relay.c
index 09b533d..1c6940d 100644
--- a/pcsc-relay/src/pcsc-relay.c
+++ b/pcsc-relay/src/pcsc-relay.c
@@ -212,7 +212,7 @@ err:
     cleanup();
 
     if (r != SCARD_S_SUCCESS) {
-        RELAY_ERROR(stringify_error(r));
+        RELAY_ERROR("%s\n", stringify_error(r));
         exit(1);
     }
 
diff --git a/virtualsmartcard/src/vpcd/ifd-vpcd.c b/virtualsmartcard/src/vpcd/ifd-vpcd.c
index 0ccdca1..caf7a43 100644
--- a/virtualsmartcard/src/vpcd/ifd-vpcd.c
+++ b/virtualsmartcard/src/vpcd/ifd-vpcd.c
@@ -167,7 +167,7 @@ IFDHPowerICC (DWORD Lun, DWORD Action, PUCHAR Atr, PDWORD AtrLength)
             }
             break;
         default:
-            Log2(PCSC_LOG_ERROR, "%d not supported", Action);
+            Log2(PCSC_LOG_ERROR, "%0lX not supported", Action);
             return IFD_NOT_SUPPORTED;
     }