diff --git a/client/emv/crypto_polarssl.c b/client/emv/crypto_polarssl.c
index 760395c4f..48e2ee4b1 100644
--- a/client/emv/crypto_polarssl.c
+++ b/client/emv/crypto_polarssl.c
@@ -215,7 +215,7 @@ static unsigned char *crypto_pk_polarssl_encrypt(const struct crypto_pk *_cp, co
 
 	res = rsa_public(&cp->ctx, buf, result);
 	if(res) {
-		printf("RSA encrypt failed. Error: %x data len: %d key len: %d\n", res * -1, len, keylen);
+		printf("RSA encrypt failed. Error: %x data len: %zu key len: %zu\n", res * -1, len, keylen);
 		return NULL;
 	}
 	
@@ -241,7 +241,7 @@ static unsigned char *crypto_pk_polarssl_decrypt(const struct crypto_pk *_cp, co
 
 	res = rsa_private(&cp->ctx, buf, result); // CHECK???
 	if(res) {
-		printf("RSA decrypt failed. Error: %x data len: %d key len: %d\n", res * -1, len, keylen);
+		printf("RSA decrypt failed. Error: %x data len: %zu key len: %zu\n", res * -1, len, keylen);
 		return NULL;
 	}
 	
diff --git a/client/emv/emv_pki.c b/client/emv/emv_pki.c
index 7803060e2..346eb9aef 100644
--- a/client/emv/emv_pki.c
+++ b/client/emv/emv_pki.c
@@ -53,7 +53,7 @@ static unsigned char *emv_pki_decode_message(const struct emv_pk *enc_pk,
 	}
 
 	if (cert_tlv->len != enc_pk->mlen) {
-		printf("ERROR: Certificate length (%d) not equal key length (%d)\n", cert_tlv->len, enc_pk->mlen);
+		printf("ERROR: Certificate length (%d) not equal key length (%zu)\n", cert_tlv->len, enc_pk->mlen);
 		return NULL;
 	}
 	kcp = crypto_pk_open(enc_pk->pk_algo,
@@ -451,7 +451,7 @@ struct tlvdb *emv_pki_perform_cda_ex(const struct emv_pk *enc_pk, const struct t
 			un_tlv,
 			NULL);
 	if (!data || data_len < 3) {
-		printf("ERROR: can't decode message. len %d\n", data_len);
+		printf("ERROR: can't decode message. len %zu\n", data_len);
 		return NULL;
 	}
 
diff --git a/client/emv/test/crypto_test.c b/client/emv/test/crypto_test.c
index e69da0a76..dee9128fe 100644
--- a/client/emv/test/crypto_test.c
+++ b/client/emv/test/crypto_test.c
@@ -219,7 +219,7 @@ static int test_pk(bool verbose)
 
 	tmp = crypto_pk_get_parameter(pubk, 0, &tmp_len);
 	if (tmp_len != sizeof(pk_N) || memcmp(tmp, pk_N, tmp_len)) {
-		fprintf(stderr, "ERROR: crypto_pk_get_parameter(0) Modulus. param len %d len %zu\n", tmp_len, sizeof(pk_N));
+		fprintf(stderr, "ERROR: crypto_pk_get_parameter(0) Modulus. param len %zu len %zu\n", tmp_len, sizeof(pk_N));
 		free(tmp);
 		goto close_pub;
 	}
@@ -256,7 +256,7 @@ static int test_pk(bool verbose)
 
 	tmp = crypto_pk_get_parameter(privk, 0, &tmp_len);
 	if (tmp_len != sizeof(pk_N) || memcmp(tmp, pk_N, tmp_len)) {
-		fprintf(stderr, "ERROR: crypto_pk_get_parameter(0) Modulus. param len %d len %zu\n", tmp_len, sizeof(pk_N));
+		fprintf(stderr, "ERROR: crypto_pk_get_parameter(0) Modulus. param len %zu len %zu\n", tmp_len, sizeof(pk_N));
 		free(tmp);
 		goto close;
 	}
diff --git a/client/util.c b/client/util.c
index dac077935..02b0e3e6c 100644
--- a/client/util.c
+++ b/client/util.c
@@ -586,7 +586,7 @@ int param_getstr(const char *line, int paramnum, char * str, size_t buffersize)
 
 	// Prevent out of bounds errors
 	if (en - bg + 1 >= buffersize) {
-		printf("out of bounds error: want %d bytes have %u bytes\n", en - bg + 1 + 1, buffersize);
+		printf("out of bounds error: want %d bytes have %zu bytes\n", en - bg + 1 + 1, buffersize);
 		return 0;
 	}
 	
@@ -622,7 +622,7 @@ int hextobinarray(char *target, char *source)
         else if (x >= 'A' && x <= 'F')
             x -= 'A' - 10;
         else {
-        	printf("Discovered unknown character %c %d at idx %d of %s\n", x, x, source - start, start);
+        	printf("Discovered unknown character %c %d at idx % " PRId32 " of %s\n", x, x, source - start, start);
             return 0;
         }
         // output