diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
index 1e874d65bfc..e9d8bbbc5d0 100644
--- a/Modules/_cursesmodule.c
+++ b/Modules/_cursesmodule.c
@@ -779,7 +779,8 @@ curses_getcchar(const cchar_t *wcval, wchar_t *wstr, attr_t *attrs, int *pair)
    when the character maps to exactly one byte, keeping the attribute and color
    bits in RTN.  A character with no single-byte form is left to winch(). */
 static chtype
-curses_cell_locale_byte(chtype rtn, const cchar_t *cell)
+curses_cell_locale_byte(PyCursesWindowObject *self, chtype rtn,
+                        const cchar_t *cell, const char *funcname)
 {
     wchar_t wstr[CCHARW_MAX + 1];
     attr_t attrs;
@@ -787,13 +788,15 @@ curses_cell_locale_byte(chtype rtn, const cchar_t *cell)
     if (curses_getcchar(cell, wstr, &attrs, &pair) == ERR
         || wstr[0] == L'\0' || wstr[1] != L'\0')
     {
-        return rtn;
+        curses_window_set_error(self, "curses_getcchar", funcname);
+        return (chtype)ERR;
     }
     /* wctob() mirrors ncurses' own _nc_to_char(): the single-byte form, or EOF
        when the character has none in this locale. */
     int byte = wctob(wstr[0]);
     if (byte != EOF) {
         rtn = (rtn & ~(chtype)A_CHARTEXT) | (unsigned char)byte;
+        assert(rtn != (chtype)ERR);
     }
     return rtn;
 }
@@ -3638,7 +3641,10 @@ _curses_window_inch_impl(PyCursesWindowObject *self, int group_right_1,
     if ((group_right_1 ? mvwin_wch(self->win, y, x, &cell)
                        : win_wch(self->win, &cell)) != ERR)
     {
-        rtn = curses_cell_locale_byte(rtn, &cell);
+        rtn = curses_cell_locale_byte(self, rtn, &cell, "inch");
+        if (rtn == (chtype)ERR) {
+            return NULL;
+        }
     }
 #endif
     return PyLong_FromUnsignedLong(rtn);