diff --git a/vendor/README.md b/vendor/README.md
index 1447f3b80..f28ea7c5c 100644
--- a/vendor/README.md
+++ b/vendor/README.md
@@ -68,6 +68,6 @@ This directory contains vendored dependencies that are shipped with InspIRCd to
 
 **License** — Boost Software License
 
-**Version** — v4.0.5
+**Version** — v4.0.6
 
 **Website** — [https://github.com/nemtrif/utfcpp](https://github.com/nemtrif/utfcpp)
diff --git a/vendor/utfcpp/core.h b/vendor/utfcpp/core.h
index 4494c538e..627133c61 100644
--- a/vendor/utfcpp/core.h
+++ b/vendor/utfcpp/core.h
@@ -215,7 +215,7 @@ namespace internal
 
         UTF8_CPP_INCREASE_AND_RETURN_ON_ERROR(it, end)
 
-        code_point += (*it) & 0x3f;
+        code_point = static_cast<utfchar32_t>(code_point + ((*it) & 0x3f));
 
         return UTF8_OK;
     }
@@ -234,11 +234,11 @@ namespace internal
 
         UTF8_CPP_INCREASE_AND_RETURN_ON_ERROR(it, end)
 
-        code_point += (utf8::internal::mask8(*it) << 6) & 0xfff;
+        code_point = static_cast<utfchar32_t>(code_point + ((utf8::internal::mask8(*it) << 6) & 0xfff));
 
         UTF8_CPP_INCREASE_AND_RETURN_ON_ERROR(it, end)
 
-        code_point += (*it) & 0x3f;
+        code_point = static_cast<utfchar32_t>(code_point + ((*it) & 0x3f));
 
         return UTF8_OK;
     }
@@ -327,7 +327,7 @@ namespace internal
             else if (is_lead_surrogate(first_word)) {
                 const utfchar16_t second_word = *it++;
                 if (is_trail_surrogate(second_word)) {
-                    code_point = (first_word << 10) + second_word + SURROGATE_OFFSET;
+                    code_point = static_cast<utfchar32_t>(first_word << 10) + second_word + SURROGATE_OFFSET;
                     return UTF8_OK;
                 } else 
                     err = INCOMPLETE_SEQUENCE; 
diff --git a/vendor/utfcpp/unchecked.h b/vendor/utfcpp/unchecked.h
index 65d4948f2..bf2917893 100644
--- a/vendor/utfcpp/unchecked.h
+++ b/vendor/utfcpp/unchecked.h
@@ -115,15 +115,15 @@ namespace utf8
                     ++it; 
                     cp = ((cp << 12) & 0xffff) + ((utf8::internal::mask8(*it) << 6) & 0xfff);
                     ++it;
-                    cp += (*it) & 0x3f;
+                    cp = static_cast<utfchar32_t>(cp + ((*it) & 0x3f));
                     break;
                 case 4:
                     ++it;
                     cp = ((cp << 18) & 0x1fffff) + ((utf8::internal::mask8(*it) << 12) & 0x3ffff);                
                     ++it;
-                    cp += (utf8::internal::mask8(*it) << 6) & 0xfff;
+                    cp = static_cast<utfchar32_t>(cp + ((utf8::internal::mask8(*it) << 6) & 0xfff));
                     ++it;
-                    cp += (*it) & 0x3f; 
+                    cp = static_cast<utfchar32_t>(cp + ((*it) & 0x3f)); 
                     break;
             }
             ++it;