diff --git a/backend/gridmtx.c b/backend/gridmtx.c
index d8193c95..5dfdd419 100644
--- a/backend/gridmtx.c
+++ b/backend/gridmtx.c
@@ -201,6 +201,7 @@ static void define_mode(unsigned int gbdata[], const size_t length, char* mode,
         if (byte_count == 512 || (double_byte && byte_count == 511)) {
             cur_costs[GM_B] = head_costs[GM_B];
             if (double_byte && byte_count == 511) {
+                cur_costs[GM_B] += 48; /* 8 * GM_MULT */
                 double_byte = 0; /* Splitting double-byte so mark as single */
             }
             byte_count = 0;
diff --git a/backend/tests/test_gridmtx.c b/backend/tests/test_gridmtx.c
index 1e9e2565..b44d3d53 100644
--- a/backend/tests/test_gridmtx.c
+++ b/backend/tests/test_gridmtx.c
@@ -156,7 +156,8 @@ static void test_input(void)
         /* 43*/ { UNICODE_MODE, 0, "AAT2556 电池充电器＋降压转换器 200mA至2A tel:86 019 82512738", 0, 0, "(62) 29 22 22 1C 4E 41 42 7E 0A 40 14 00 37 7E 6F 00 62 7E 2C 00 1C 7E 4B 00 41 7E 18 00 42 7E 61", "M8 H11 M6 B4 L5(with control) N15 (GB 2312) (*NOT SAME* as D3 example, M8 H11 M6 H1 M3 L4(with control) N15, which uses a few more bits)" },
         /* 44*/ { UNICODE_MODE, 0, "::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::", 0, 0, "(588) 37 68 68 68 68 68 74 7E 74 74 74 74 74 3A 3A 3A 3A 3A 3A 3A 1D 1D 1D 1D 1D 1D 1D 0E 0E 0E 0E", "B512 (ASCII)" },
         /* 45*/ { UNICODE_MODE, 0, "::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::\177", 0, 0, "(591) 37 68 68 68 68 68 74 7E 74 74 74 74 74 3A 3A 3A 3A 3A 3A 3A 1D 1D 1D 1D 1D 1D 1D 0E 0E 0E 0E", "B513 (ASCII)" },
-        /* 46*/ { UNICODE_MODE, 0, ":::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::至", 0, 0, "(591) 37 68 68 68 68 68 74 7E 74 74 74 74 74 3A 3A 3A 3A 3A 3A 3A 1D 1D 1D 1D 1D 1D 1D 0E 0E 0E 0E", "B513 (GB 2312)" },
+        /* 46*/ { UNICODE_MODE, 0, ":::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::至", 0, 0, "(591) 37 68 68 68 68 68 74 7C 74 74 74 74 74 3A 3A 3A 3A 3A 3A 3A 1D 1D 1D 1D 1D 1D 1D 0E 0E 0E 0E", "B511 H1 (GB 2312)" },
+        /* 47*/ { UNICODE_MODE, 0, ":::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::至:", 0, 0, "(592) 37 68 68 68 68 68 74 7E 74 74 74 74 74 3A 3A 3A 3A 3A 3A 3A 1D 1D 1D 1D 1D 1D 1D 0E 0E 0E 0E", "B513 (GB 2312)" },
     };
     int data_size = sizeof(data) / sizeof(struct item);