diff --git a/win32ss/user/user32/controls/edit.c b/win32ss/user/user32/controls/edit.c
index 1eccfbf168..43e99f345f 100644
--- a/win32ss/user/user32/controls/edit.c
+++ b/win32ss/user/user32/controls/edit.c
@@ -2907,6 +2907,40 @@ static void EDIT_EM_SetLimitText(EDITSTATE *es, UINT limit)
     es->buffer_limit = limit;
 }
 
+static BOOL is_cjk_charset(HDC dc)
+{
+    switch (GdiGetCodePage(dc)) {
+    case 932: case 936: case 949: case 950: case 1361:
+        return TRUE;
+    default:
+        return FALSE;
+    }
+}
+
+static BOOL is_cjk_font(HDC dc)
+{
+    const DWORD FS_DBCS_MASK = FS_JISJAPAN|FS_CHINESESIMP|FS_WANSUNG|FS_CHINESETRAD|FS_JOHAB;
+    FONTSIGNATURE fs;
+    return (GetTextCharsetInfo(dc, &fs, 0) != DEFAULT_CHARSET &&
+            (fs.fsCsb[0] & FS_DBCS_MASK));
+}
+
+static int get_cjk_fontinfo_margin(int width, int side_bearing)
+{
+    int margin;
+    if (side_bearing < 0)
+        margin = min(-side_bearing, width/2);
+    else
+        margin = 0;
+    return margin;
+}
+
+struct char_width_info {
+    INT min_lsb, min_rsb, unknown;
+};
+
+/* Undocumented gdi32 export */
+extern BOOL WINAPI GetCharWidthInfo(HDC, struct char_width_info *);
 
 /*********************************************************************
  *
@@ -2921,20 +2955,6 @@ static void EDIT_EM_SetLimitText(EDITSTATE *es, UINT limit)
  * size.  Though there is an exception for the empty client rect case
  * with small font sizes.
  */
-static BOOL is_cjk(UINT charset)
-{
-    switch(charset)
-    {
-    case SHIFTJIS_CHARSET:
-    case HANGUL_CHARSET:
-    case GB2312_CHARSET:
-    case CHINESEBIG5_CHARSET:
-        return TRUE;
-    }
-    /* HANGUL_CHARSET is strange, though treated as CJK by Win 8, it is
-     * not by other versions including Win 10. */
-    return FALSE;
-}
 
 static void EDIT_EM_SetMargins(EDITSTATE *es, INT action,
 			       WORD left, WORD right, BOOL repaint)
@@ -2947,26 +2967,31 @@ static void EDIT_EM_SetMargins(EDITSTATE *es, INT action,
         if (es->font && (left == EC_USEFONTINFO || right == EC_USEFONTINFO)) {
             HDC dc = GetDC(es->hwndSelf);
             HFONT old_font = SelectObject(dc, es->font);
-            LONG width = GdiGetCharDimensions(dc, &tm, NULL);
+            LONG width = GdiGetCharDimensions(dc, &tm, NULL), rc_width;
             RECT rc;
 
             /* The default margins are only non zero for TrueType or Vector fonts */
             if (tm.tmPitchAndFamily & ( TMPF_VECTOR | TMPF_TRUETYPE )) {
-                if (!is_cjk(tm.tmCharSet)) {
-                    default_left_margin = width / 2;
-                    default_right_margin = width / 2;
+                struct char_width_info width_info;
 
-                    GetClientRect(es->hwndSelf, &rc);
-                    if (rc.right - rc.left < (width / 2 + width) * 2 &&
-                        (width >= 28 || !IsRectEmpty(&rc)) ) {
-                        default_left_margin = es->left_margin;
-                        default_right_margin = es->right_margin;
-                    }
-                } else {
-                    /* FIXME: figure out the CJK values. They are not affected by the client rect. */
+                if ((is_cjk_charset(dc) || is_cjk_font(dc)) &&
+                    GetCharWidthInfo(dc, &width_info))
+                {
+                    default_left_margin = get_cjk_fontinfo_margin(width, width_info.min_lsb);
+                    default_right_margin = get_cjk_fontinfo_margin(width, width_info.min_rsb);
+                }
+                else
+                {
                     default_left_margin = width / 2;
                     default_right_margin = width / 2;
                 }
+
+                GetClientRect(es->hwndSelf, &rc);
+                rc_width = !IsRectEmpty(&rc) ? rc.right - rc.left : 80;
+                if (rc_width < default_left_margin + default_right_margin + width * 2) {
+                    default_left_margin = es->left_margin;
+                    default_right_margin = es->right_margin;
+                }
             }
             SelectObject(dc, old_font);
             ReleaseDC(es->hwndSelf, dc);