diff --git a/source/utf8/checked.h b/source/utf8/checked.h
index 2aef583..7151370 100644
--- a/source/utf8/checked.h
+++ b/source/utf8/checked.h
@@ -257,8 +257,17 @@ namespace utf8
     template <typename octet_iterator, typename u32bit_iterator>
     u32bit_iterator utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result)
     {
-        while (start < end)
-            (*result++) = utf8::next(start, end);
+        uint32_t ch1, ch2;
+        while (start < end) {
+            ch1 = utf8::next(start, end);
+            if (internal::is_lead_surrogate(ch1) && start < end) {
+                ch2 = utf8::next(start, end);
+                *(result++) = ((ch1 - internal::LEAD_SURROGATE_MIN) << 10) + ch2 - internal::TRAIL_SURROGATE_MIN;
+            }
+            else {
+                *(result++) = ch1;
+            }
+        }
 
         return result;
     }
diff --git a/source/utf8/core.h b/source/utf8/core.h
index ae0f367..dab6fed 100644
--- a/source/utf8/core.h
+++ b/source/utf8/core.h
@@ -92,7 +92,7 @@ namespace internal
     template <typename u32>
     inline bool is_code_point_valid(u32 cp)
     {
-        return (cp <= CODE_POINT_MAX && !utf8::internal::is_surrogate(cp));
+        return cp <= CODE_POINT_MAX;
     }
 
     template <typename octet_iterator>
diff --git a/source/utf8/unchecked.h b/source/utf8/unchecked.h
index cb24271..731f636 100644
--- a/source/utf8/unchecked.h
+++ b/source/utf8/unchecked.h
@@ -168,8 +168,17 @@ namespace utf8
         template <typename octet_iterator, typename u32bit_iterator>
         u32bit_iterator utf8to32 (octet_iterator start, octet_iterator end, u32bit_iterator result)
         {
-            while (start < end)
-                (*result++) = utf8::unchecked::next(start);
+            uint32_t ch1, ch2;
+            while (start < end) {
+                ch1 = utf8::unchecked::next(start);
+                if (internal::is_lead_surrogate(ch1) && start < end) {
+                    ch2 = utf8::unchecked::next(start);
+                    *(result++) = ((ch1 - internal::LEAD_SURROGATE_MIN) << 10) + ch2 - internal::TRAIL_SURROGATE_MIN;
+                }
+                else {
+                    *(result++) = ch1;
+                }
+            }
 
             return result;
         }