diff --git a/CMakeLists.txt b/CMakeLists.txt
index 019a78c..8a7f659 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -39,6 +39,10 @@ set( CMAKE_CXX_STANDARD 11 )
 set( CMAKE_CXX_STANDARD_REQUIRED ON )
 set( CMAKE_CXX_EXTENSIONS OFF )
 
+if (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+	set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror -Wall -Wconversion -Wno-sign-conversion -Wextra" )
+endif()
+
 # Libraries
 find_package(OpenSSL 1.1 REQUIRED)
 
diff --git a/src/base58.cpp b/src/base58.cpp
index 38304c7..cd3eccd 100644
--- a/src/base58.cpp
+++ b/src/base58.cpp
@@ -24,6 +24,7 @@
  *
  * Based on code from https://github.com/bitcoin/bitcoin/blob/f1e2f2a85962c1664e4e55471061af0eaa798d40/src/base58.cpp
  */
+#include <cstddef>
 #include <cassert>
 #include "base58.h"
 
@@ -39,7 +40,7 @@ std::string base58_encode(const unsigned char* pbegin, const unsigned char* pend
         zeroes++;
     }
     // Allocate enough space in big-endian base58 representation.
-    int size = (pend - pbegin) * 138 / 100 + 1; // log(256) / log(58), rounded up.
+    std::size_t size = (pend - pbegin) * 138 / 100 + 1; // log(256) / log(58), rounded up.
     std::vector<unsigned char> b58(size);
     // Process the bytes.
     while (pbegin != pend) {
@@ -48,7 +49,7 @@ std::string base58_encode(const unsigned char* pbegin, const unsigned char* pend
         // Apply "b58 = b58 * 256 + ch".
         for (std::vector<unsigned char>::reverse_iterator it = b58.rbegin(); (carry != 0 || i < length) && (it != b58.rend()); it++, i++) {
             carry += 256 * (*it);
-            *it = carry % 58;
+            *it = static_cast<unsigned char>(carry % 58);
             carry /= 58;
         }
 
diff --git a/src/checksum.cpp b/src/checksum.cpp
index 3c29dcb..53c7e33 100644
--- a/src/checksum.cpp
+++ b/src/checksum.cpp
@@ -26,13 +26,13 @@
 #include <cstring>
 #include "checksum.h"
 
-inline void sha256d(const unsigned char *data, unsigned int len, unsigned char *out) {
+inline void sha256d(const unsigned char *data, std::size_t len, unsigned char *out) {
 	SHA256(data, len, out);
 	SHA256(out, 32, out);
 }
 
 #define checksum_impl(name, func) \
-	checksum_t checksum_##name(const unsigned char *data, unsigned int len) { 	\
+	checksum_t checksum_##name(const unsigned char *data, std::size_t len) { 	\
 																				\
 		checksum_t crc;															\
 		unsigned char hash[32];													\
diff --git a/src/checksum.h b/src/checksum.h
index 44bfef8..57f50e8 100644
--- a/src/checksum.h
+++ b/src/checksum.h
@@ -24,12 +24,13 @@
 #ifndef CHECKSUM_H
 #define CHECKSUM_H
 
+#include <cstddef>
 #include <array>
 
 typedef std::array<unsigned char, 4> checksum_t;
 
-checksum_t checksum_sha256d(const unsigned char *data, unsigned int len);
+checksum_t checksum_sha256d(const unsigned char *data, std::size_t len);
 
-checksum_t checksum_ripemd160(const unsigned char *data, unsigned int len);
+checksum_t checksum_ripemd160(const unsigned char *data, std::size_t len);
 
 #endif /* CHECKSUM_H */
diff --git a/src/key_search_mt.cpp b/src/key_search_mt.cpp
index 881ed53..e3d22cc 100644
--- a/src/key_search_mt.cpp
+++ b/src/key_search_mt.cpp
@@ -1,4 +1,5 @@
 
+#include <cstddef>
 #include <thread>
 #include <mutex>
 #include <vector>
@@ -7,10 +8,10 @@
 #include "key_search.h"
 
 // Max keys to search for,
-unsigned int g_max;
+std::size_t g_max;
 
 // How many keys we have found so far.
-unsigned int g_count;
+std::size_t g_count;
 
 // Mutex guard for g_count.
 std::mutex g_count_mtx;
@@ -60,7 +61,7 @@ void KeySearch::_search_mt(size_t n)
 	g_count = 0;
 
 	// Launch them.
-	for(int i = 0; i < t.size(); i++) {
+	for(std::size_t i = 0; i < t.size(); i++) {
 		t[i] = std::thread(_thr_proc, m_words);
 	}
 
@@ -68,7 +69,7 @@ void KeySearch::_search_mt(size_t n)
 	_thr_proc(m_words);
 
 	// Wait for all threads to compelete.
-	for(int i = 0; i < t.size(); i++) {
+	for(std::size_t i = 0; i < t.size(); i++) {
 		t[i].join();
 	}
 }
diff --git a/src/main.cpp b/src/main.cpp
index a68eed7..fa4d050 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -46,7 +46,7 @@ void cmd_search(int argc, char **argv) {
 
 	if (option_l33t) {
 		strlist_t tmp = strsplitwords(input);
-		for(int i = 0; i < tmp.size(); i++) {
+		for(std::size_t i = 0; i < tmp.size(); i++) {
 			ks.addList(l33twords(tmp[i]));
 		}
 	} else {
diff --git a/src/string.cpp b/src/string.cpp
index 8793fa1..bee3330 100644
--- a/src/string.cpp
+++ b/src/string.cpp
@@ -21,8 +21,9 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */
-#include <algorithm>
+#include <cstddef>
 #include <cctype>
+#include <algorithm>
 #include "string.h"
 
 strlist_t strsplitwords(const std::string& str, const std::string& delim) {
@@ -108,20 +109,20 @@ static bool is_l33t(char ch, char& r) {
 	//                          '1', '2', '3', '4', '5', '6', '7', '8', '9'
 	static char alphabet[9] = { 'l', 'z', 'e', 'a', 's', 'G', 't', 'B', 'g' };
 
-	for(int i = 0; i < sizeof(alphabet) / sizeof(char); i++) {
+	for(std::size_t i = 0; i < sizeof(alphabet) / sizeof(char); i++) {
 
 		if (ch == alphabet[i]) {
-			r = '1' + i;
+			r = static_cast<char>('1' + i);
 			return true;
 		}
 	}
 	return false;
 }
 
-static void _l33t(strlist_t& list, const std::string& a, int pos) {
+static void _l33t(strlist_t& list, const std::string& a, std::size_t pos) {
 
 	// Find the next character to be replaced.
-	for(int i = pos; i < a.length(); i++) {
+	for(std::size_t i = pos; i < a.length(); i++) {
 
 		char ch;
 		if (is_l33t(a[i], ch)) {