diff --git a/storage/innobase/dict/dict0dict.c b/storage/innobase/dict/dict0dict.c
index 6f2c2caffaf..a8b0c33f2c0 100644
--- a/storage/innobase/dict/dict0dict.c
+++ b/storage/innobase/dict/dict0dict.c
@@ -2017,7 +2017,6 @@ dict_index_build_internal_clust(
 {
 	dict_index_t*	new_index;
 	dict_field_t*	field;
-	ulint		fixed_size;
 	ulint		trx_id_pos;
 	ulint		i;
 	ibool*		indexed;
@@ -2094,7 +2093,7 @@ dict_index_build_internal_clust(
 
 		for (i = 0; i < trx_id_pos; i++) {
 
-			fixed_size = dict_col_get_fixed_size(
+			ulint	fixed_size = dict_col_get_fixed_size(
 				dict_index_get_nth_col(new_index, i),
 				dict_table_is_comp(table));
 
@@ -2111,7 +2110,20 @@ dict_index_build_internal_clust(
 				break;
 			}
 
-			new_index->trx_id_offset += (unsigned int) fixed_size;
+			/* Add fixed_size to new_index->trx_id_offset.
+			Because the latter is a bit-field, an overflow
+			can theoretically occur. Check for it. */
+			fixed_size += new_index->trx_id_offset;
+
+			new_index->trx_id_offset = fixed_size;
+
+			if (new_index->trx_id_offset != fixed_size) {
+				/* Overflow. Pretend that this is a
+				variable-length PRIMARY KEY. */
+				ut_ad(0);
+				new_index->trx_id_offset = 0;
+				break;
+			}
 		}
 
 	}
diff --git a/storage/innobase/include/dict0mem.h b/storage/innobase/include/dict0mem.h
index 4c371c8d5cf..980417715b3 100644
--- a/storage/innobase/include/dict0mem.h
+++ b/storage/innobase/include/dict0mem.h
@@ -377,10 +377,15 @@ struct dict_index_struct{
 	unsigned	type:DICT_IT_BITS;
 				/*!< index type (DICT_CLUSTERED, DICT_UNIQUE,
 				DICT_UNIVERSAL, DICT_IBUF, DICT_CORRUPT) */
-	unsigned	trx_id_offset:10;/*!< position of the trx id column
+#define MAX_KEY_LENGTH_BITS 12
+	unsigned	trx_id_offset:MAX_KEY_LENGTH_BITS;
+				/*!< position of the trx id column
 				in a clustered index record, if the fields
 				before it are known to be of a fixed size,
 				0 otherwise */
+#if (1<<MAX_KEY_LENGTH_BITS) < MAX_KEY_LENGTH
+# error (1<<MAX_KEY_LENGTH_BITS) < MAX_KEY_LENGTH
+#endif
 	unsigned	n_user_defined_cols:10;
 				/*!< number of columns the user defined to
 				be in the index: in the internal
diff --git a/storage/innobase/include/row0upd.ic b/storage/innobase/include/row0upd.ic
index 10646241125..6706c9f8c69 100644
--- a/storage/innobase/include/row0upd.ic
+++ b/storage/innobase/include/row0upd.ic
@@ -28,6 +28,7 @@ Created 12/27/1996 Heikki Tuuri
 # include "trx0trx.h"
 # include "trx0undo.h"
 # include "row0row.h"
+# include "lock0lock.h"
 #endif /* !UNIV_HOTBACKUP */
 #include "page0zip.h"
 
@@ -171,6 +172,8 @@ row_upd_rec_sys_fields(
 #if DATA_TRX_ID + 1 != DATA_ROLL_PTR
 # error "DATA_TRX_ID + 1 != DATA_ROLL_PTR"
 #endif
+		ut_ad(lock_check_trx_id_sanity(trx_read_trx_id(rec + offset),
+					       rec, index, offsets, FALSE));
 		trx_write_trx_id(rec + offset, trx->id);
 		trx_write_roll_ptr(rec + offset + DATA_TRX_ID_LEN, roll_ptr);
 	}