diff --git a/examples/dctool_parse.c b/examples/dctool_parse.c
index 6ea8550..6b7da08 100644
--- a/examples/dctool_parse.c
+++ b/examples/dctool_parse.c
@@ -152,7 +152,7 @@ dctool_parse_run (int argc, char *argv[], dc_context_t *context, dc_descriptor_t
 		goto cleanup;
 	}
 
-	for (unsigned int i = 0; i < argc; ++i) {
+	for (int i = 0; i < argc; ++i) {
 		// Read the input file.
 		buffer = dctool_file_read (argv[i]);
 		if (buffer == NULL) {
diff --git a/examples/output_raw.c b/examples/output_raw.c
index 951531e..9e71780 100644
--- a/examples/output_raw.c
+++ b/examples/output_raw.c
@@ -80,7 +80,7 @@ mktemplate_datetime (char *buffer, size_t size, dc_parser_t *parser)
 	n = snprintf (buffer, size, "%04i%02i%02iT%02i%02i%02i",
 		datetime.year, datetime.month, datetime.day,
 		datetime.hour, datetime.minute, datetime.second);
-	if (n < 0 || n >= size)
+	if (n < 0 || (size_t) n >= size)
 		return -1;
 
 	return n;
@@ -92,7 +92,7 @@ mktemplate_number (char *buffer, size_t size, unsigned int number)
 	int n = 0;
 
 	n = snprintf (buffer, size, "%04u", number);
-	if (n < 0 || n >= size)
+	if (n < 0 || (size_t) n >= size)
 		return -1;
 
 	return n;
diff --git a/src/context.c b/src/context.c
index 88fd9b5..cab6f33 100644
--- a/src/context.c
+++ b/src/context.c
@@ -77,7 +77,7 @@ l_vsnprintf (char *str, size_t size, const char *format, va_list ap)
 	 * enough.
 	 */
 	n = vsnprintf (str, size, format, ap);
-	if (n >= size)
+	if (n >= 0 && (size_t) n >= size)
 		n = -1;
 #endif
 
diff --git a/src/hw_ostc3.c b/src/hw_ostc3.c
index c669ea2..3ed6bc7 100644
--- a/src/hw_ostc3.c
+++ b/src/hw_ostc3.c
@@ -1024,7 +1024,7 @@ hw_ostc3_firmware_readline (FILE *fp, dc_context_t *context, unsigned int addr,
 	unsigned char ascii[39];
 	unsigned char faddr_byte[3];
 	unsigned int faddr = 0;
-	int n = 0;
+	size_t n = 0;
 
 	if (size > 16) {
 		ERROR (context, "Invalid arguments.");
diff --git a/src/suunto_d9.c b/src/suunto_d9.c
index ab6eee1..8b8320e 100644
--- a/src/suunto_d9.c
+++ b/src/suunto_d9.c
@@ -261,7 +261,8 @@ suunto_d9_device_packet (dc_device_t *abstract, const unsigned char command[], u
 	}
 
 	// Verify the size of the package.
-	if (array_uint16_be (answer + 1) + 4 != asize) {
+	unsigned int len = array_uint16_be (answer + 1);
+	if (len + 4 != asize) {
 		ERROR (abstract->context, "Unexpected answer size.");
 		return DC_STATUS_PROTOCOL;
 	}
diff --git a/src/suunto_eonsteel_parser.c b/src/suunto_eonsteel_parser.c
index d8dcdcc..a941518 100644
--- a/src/suunto_eonsteel_parser.c
+++ b/src/suunto_eonsteel_parser.c
@@ -137,7 +137,6 @@ static const struct {
 
 static enum eon_sample lookup_descriptor_type(suunto_eonsteel_parser_t *eon, struct type_desc *desc)
 {
-	int i;
 	const char *name = desc->desc;
 
 	// Not a sample type? Skip it
@@ -160,7 +159,7 @@ static enum eon_sample lookup_descriptor_type(suunto_eonsteel_parser_t *eon, str
 	name += 8;
 
 	// .. and look it up in the table of sample type strings
-	for (i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
+	for (size_t i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
 		if (!strcmp(name, type_translation[i].name))
 			return type_translation[i].type;
 	}
@@ -179,8 +178,7 @@ static parser_sample_event_t lookup_event(const char *name, const eon_event_t ev
 
 static const char *desc_type_name(enum eon_sample type)
 {
-	int i;
-	for (i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
+	for (size_t i = 0; i < C_ARRAY_SIZE(type_translation); i++) {
 		if (type == type_translation[i].type)
 			return type_translation[i].name;
 	}
diff --git a/src/suunto_vyper2.c b/src/suunto_vyper2.c
index 02f38ed..7a9f7ce 100644
--- a/src/suunto_vyper2.c
+++ b/src/suunto_vyper2.c
@@ -252,7 +252,8 @@ suunto_vyper2_device_packet (dc_device_t *abstract, const unsigned char command[
 	}
 
 	// Verify the size of the package.
-	if (array_uint16_be (answer + 1) + 4 != asize) {
+	unsigned int len = array_uint16_be (answer + 1);
+	if (len + 4 != asize) {
 		ERROR (abstract->context, "Unexpected answer size.");
 		return DC_STATUS_PROTOCOL;
 	}
diff --git a/src/usbhid.c b/src/usbhid.c
index 9231e64..b3805ca 100644
--- a/src/usbhid.c
+++ b/src/usbhid.c
@@ -777,7 +777,7 @@ dc_usbhid_write (dc_iostream_t *abstract, const void *data, size_t size, size_t
 
 out:
 #ifdef _WIN32
-	if (nbytes > size) {
+	if ((size_t) nbytes > size) {
 		WARNING (abstract->context, "Number of bytes exceeds the buffer size (" DC_PRINTF_SIZE " > " DC_PRINTF_SIZE ")!", nbytes, size);
 		nbytes = size;
 	}