@@ -1,7 +1,7 @@
 /* -*- mode: c++; c-basic-offset: 4 -*- */
 
 #include <algorithm>
-#include <charconv>
+#include <cstdio>
 #include <iterator>
 #include <set>
 #include <sstream>
@@ -727,13 +727,20 @@ void FT2Font::get_glyph_name(unsigned int glyph_number, std::string &buffer,
     if (!FT_HAS_GLYPH_NAMES(face)) {
         /* Note that this generated name must match the name that
            is generated by ttconv in ttfont_CharStrings_getname. */
-        buffer.replace(0, 3, "uni");
-        std::to_chars(buffer.data() + 3, buffer.data() + buffer.size(),
-                      glyph_number, 16);
+        auto len = snprintf(buffer.data(), buffer.size(), "uni%08x", glyph_number);
+        if (len >= 0) {
+            buffer.resize(len);
+        } else {
+            throw std::runtime_error("Failed to convert glyph to standard name");
+        }
     } else {
         if (FT_Error error = FT_Get_Glyph_Name(face, glyph_number, buffer.data(), buffer.size())) {
             throw_ft_error("Could not get glyph names", error);
         }
+        auto len = buffer.find('\0');
+        if (len != buffer.npos) {
+            buffer.resize(len);
+        }
     }
 }
 
 
@@ -486,11 +486,6 @@ PyFT2Font_get_glyph_name(PyFT2Font *self, unsigned int glyph_number)
 
     buffer.resize(128);
     self->x->get_glyph_name(glyph_number, buffer, fallback);
-    // pybind11 uses the entire string's size(), so trim all the NULLs off the end.
-    auto len = buffer.find('\0');
-    if (len != buffer.npos) {
-        buffer.resize(len);
-    }
     return buffer;
 }