diff --git a/contrib/epee/include/net/http_client.h b/contrib/epee/include/net/http_client.h
index 6396bbe6f..6e49f5f42 100644
--- a/contrib/epee/include/net/http_client.h
+++ b/contrib/epee/include/net/http_client.h
@@ -662,14 +662,14 @@ namespace net_utils
 				ptr = end + 1;
 				CHECK_AND_ASSERT_MES(epee::misc_utils::parse::isdigit(*ptr), false, "Invalid first response line: " + m_header_cache + ", ptr: " << ptr);
 				ul = strtoul(ptr, &end, 10);
-				CHECK_AND_ASSERT_MES(ul <= INT_MAX && isblank(*end), false, "Invalid first response line: " + m_header_cache + ", ptr: " << ptr);
+				CHECK_AND_ASSERT_MES(ul <= INT_MAX && isblank(static_cast<unsigned char>(*end)), false, "Invalid first response line: " + m_header_cache + ", ptr: " << ptr);
 				m_response_info.m_http_ver_lo = ul;
 				ptr = end + 1;
-				while (isblank(*ptr))
+				while (isblank(static_cast<unsigned char>(*ptr)))
 					++ptr;
 				CHECK_AND_ASSERT_MES(epee::misc_utils::parse::isdigit(*ptr), false, "Invalid first response line: " + m_header_cache);
 				ul = strtoul(ptr, &end, 10);
-				CHECK_AND_ASSERT_MES(ul >= 100 && ul <= 999 && isspace(*end), false, "Invalid first response line: " + m_header_cache);
+				CHECK_AND_ASSERT_MES(ul >= 100 && ul <= 999 && isspace(static_cast<unsigned char>(*end)), false, "Invalid first response line: " + m_header_cache);
 				m_response_info.m_response_code = ul;
 				ptr = end;
 				// ignore the optional text, till the end
diff --git a/contrib/epee/src/abstract_http_client.cpp b/contrib/epee/src/abstract_http_client.cpp
index bd9cb0dde..dd3763ad1 100644
--- a/contrib/epee/src/abstract_http_client.cpp
+++ b/contrib/epee/src/abstract_http_client.cpp
@@ -65,8 +65,8 @@ namespace net_utils
   std::string hex_to_dec_2bytes(const char *s)
   {
     const char *hex = get_hex_vals();
-    int i0 = get_index(hex, toupper(s[0]));
-    int i1 = get_index(hex, toupper(s[1]));
+    int i0 = get_index(hex, toupper(static_cast<unsigned char>(s[0])));
+    int i1 = get_index(hex, toupper(static_cast<unsigned char>(s[1])));
     if (i0 < 0 || i1 < 0)
       return std::string("%") + std::string(1, s[0]) + std::string(1, s[1]);
     return std::string(1, i0 * 16 | i1);
diff --git a/src/common/updates.cpp b/src/common/updates.cpp
index a8202b0d5..6c445ca54 100644
--- a/src/common/updates.cpp
+++ b/src/common/updates.cpp
@@ -73,7 +73,7 @@ namespace tools
 
       bool alnum = true;
       for (auto c: fields[3])
-        if (!isalnum(c))
+        if (!isalnum(static_cast<unsigned char>(c)))
           alnum = false;
       if (fields[3].size() != 64 && !alnum)
       {