diff --git a/src/blob.c b/src/blob.c
index 114dacd..9f59777 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -125,13 +125,33 @@
 }
 
 /*
- * Store one byte "c" in blob "b" at "idx".
+ * Store one byte "byte" in blob "blob" at "idx".
  * Caller must make sure that "idx" is valid.
  */
     void
-blob_set(blob_T *b, int idx, char_u c)
+blob_set(blob_T *blob, int idx, int byte)
 {
-    ((char_u*)b->bv_ga.ga_data)[idx] = c;
+    ((char_u*)blob->bv_ga.ga_data)[idx] = byte;
+}
+
+/*
+ * Store one byte "byte" in blob "blob" at "idx".
+ * Append one byte if needed.
+ */
+    void
+blob_set_append(blob_T *blob, int idx, int byte)
+{
+    garray_T *gap = &blob->bv_ga;
+
+    // Allow for appending a byte.  Setting a byte beyond
+    // the end is an error otherwise.
+    if (idx < gap->ga_len
+	    || (idx == gap->ga_len && ga_grow(gap, 1) == OK))
+    {
+	blob_set(blob, idx, byte);
+	if (idx == gap->ga_len)
+	    ++gap->ga_len;
+    }
 }
 
 /*
diff --git a/src/errors.h b/src/errors.h
index 99f3aaf..1e09186 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -403,3 +403,5 @@
 	INIT(= N_("E1182: Blob required"));
 EXTERN char e_cannot_use_range_with_assignment_operator_str[]
 	INIT(= N_("E1183: Cannot use a range with an assignment operator: %s"));
+EXTERN char e_blob_not_set[]
+	INIT(= N_("E1184: Blob not set"));
diff --git a/src/proto/blob.pro b/src/proto/blob.pro
index 3adaf0f..157f15b 100644
--- a/src/proto/blob.pro
+++ b/src/proto/blob.pro
@@ -7,7 +7,8 @@
 void blob_unref(blob_T *b);
 long blob_len(blob_T *b);
 int blob_get(blob_T *b, int idx);
-void blob_set(blob_T *b, int idx, char_u c);
+void blob_set(blob_T *blob, int idx, int byte);
+void blob_set_append(blob_T *blob, int idx, int byte);
 int blob_equal(blob_T *b1, blob_T *b2);
 int read_blob(FILE *fd, blob_T *blob);
 int write_blob(FILE *fd, blob_T *blob);
diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index 3699f3b..21f90ef 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -120,88 +120,166 @@
 endfunc
 
 func Test_blob_get_range()
+  let lines =<< trim END
+      VAR b = 0z0011223344
+      call assert_equal(0z2233, b[2 : 3])
+      call assert_equal(0z223344, b[2 : -1])
+      call assert_equal(0z00, b[0 : -5])
+      call assert_equal(0z, b[0 : -11])
+      call assert_equal(0z44, b[-1 :])
+      call assert_equal(0z0011223344, b[:])
+      call assert_equal(0z0011223344, b[: -1])
+      call assert_equal(0z, b[5 : 6])
+      call assert_equal(0z0011, b[-10 : 1])
+  END
+  call CheckLegacyAndVim9Success(lines)
+
+  " legacy script white space
   let b = 0z0011223344
   call assert_equal(0z2233, b[2:3])
-  call assert_equal(0z223344, b[2:-1])
-  call assert_equal(0z00, b[0:-5])
-  call assert_equal(0z, b[0:-11])
-  call assert_equal(0z44, b[-1:])
-  call assert_equal(0z0011223344, b[:])
-  call assert_equal(0z0011223344, b[:-1])
-  call assert_equal(0z, b[5:6])
-  call assert_equal(0z0011, b[-10:1])
 endfunc
 
 func Test_blob_get()
-  let b = 0z0011223344
-  call assert_equal(0x00, get(b, 0))
-  call assert_equal(0x22, get(b, 2, 999))
-  call assert_equal(0x44, get(b, 4))
-  call assert_equal(0x44, get(b, -1))
-  call assert_equal(-1, get(b, 5))
-  call assert_equal(999, get(b, 5, 999))
-  call assert_equal(-1, get(b, -8))
-  call assert_equal(999, get(b, -8, 999))
-  call assert_equal(10, get(test_null_blob(), 2, 10))
+  let lines =<< trim END
+      VAR b = 0z0011223344
+      call assert_equal(0x00, get(b, 0))
+      call assert_equal(0x22, get(b, 2, 999))
+      call assert_equal(0x44, get(b, 4))
+      call assert_equal(0x44, get(b, -1))
+      call assert_equal(-1, get(b, 5))
+      call assert_equal(999, get(b, 5, 999))
+      call assert_equal(-1, get(b, -8))
+      call assert_equal(999, get(b, -8, 999))
+      call assert_equal(10, get(test_null_blob(), 2, 10))
 
-  call assert_equal(0x00, b[0])
-  call assert_equal(0x22, b[2])
-  call assert_equal(0x44, b[4])
-  call assert_equal(0x44, b[-1])
-  call assert_fails('echo b[5]', 'E979:')
-  call assert_fails('echo b[-8]', 'E979:')
+      call assert_equal(0x00, b[0])
+      call assert_equal(0x22, b[2])
+      call assert_equal(0x44, b[4])
+      call assert_equal(0x44, b[-1])
+  END
+  call CheckLegacyAndVim9Success(lines)
+
+  let lines =<< trim END
+      VAR b = 0z0011223344
+      echo b[5]
+  END
+  call CheckLegacyAndVim9Failure(lines, 'E979:')
+
+  let lines =<< trim END
+      VAR b = 0z0011223344
+      echo b[-8]
+  END
+  call CheckLegacyAndVim9Failure(lines, 'E979:')
 endfunc
 
 func Test_blob_to_string()
-  let b = 0z00112233445566778899aabbccdd
-  call assert_equal('0z00112233.44556677.8899AABB.CCDD', string(b))
-  call assert_equal(b, eval(string(b)))
-  call remove(b, 4, -1)
-  call assert_equal('0z00112233', string(b))
-  call remove(b, 0, 3)
-  call assert_equal('0z', string(b))
-  call assert_equal('0z', string(test_null_blob()))
+  let lines =<< trim END
+      VAR b = 0z00112233445566778899aabbccdd
+      call assert_equal('0z00112233.44556677.8899AABB.CCDD', string(b))
+      call assert_equal(b, eval(string(b)))
+      call remove(b, 4, -1)
+      call assert_equal('0z00112233', string(b))
+      call remove(b, 0, 3)
+      call assert_equal('0z', string(b))
+      call assert_equal('0z', string(test_null_blob()))
+  END
+  call CheckLegacyAndVim9Success(lines)
 endfunc
 
 func Test_blob_compare()
-  let b1 = 0z0011
-  let b2 = 0z1100
-  let b3 = 0z001122
-  call assert_true(b1 == b1)
-  call assert_false(b1 == b2)
-  call assert_false(b1 == b3)
-  call assert_true(b1 != b2)
-  call assert_true(b1 != b3)
-  call assert_true(b1 == 0z0011)
-  call assert_fails('echo b1 == 9', 'E977:')
-  call assert_fails('echo b1 != 9', 'E977:')
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      VAR b2 = 0z1100
+      VAR b3 = 0z001122
+      call assert_true(b1 == b1)
+      call assert_false(b1 == b2)
+      call assert_false(b1 == b3)
+      call assert_true(b1 != b2)
+      call assert_true(b1 != b3)
+      call assert_true(b1 == 0z0011)
 
-  call assert_false(b1 is b2)
-  let b2 = b1
-  call assert_true(b1 == b2)
-  call assert_true(b1 is b2)
-  let b2 = copy(b1)
-  call assert_true(b1 == b2)
-  call assert_false(b1 is b2)
-  let b2 = b1[:]
-  call assert_true(b1 == b2)
-  call assert_false(b1 is b2)
-  call assert_true(b1 isnot b2)
+      call assert_false(b1 is b2)
+      LET b2 = b1
+      call assert_true(b1 == b2)
+      call assert_true(b1 is b2)
+      LET b2 = copy(b1)
+      call assert_true(b1 == b2)
+      call assert_false(b1 is b2)
+      LET b2 = b1[:]
+      call assert_true(b1 == b2)
+      call assert_false(b1 is b2)
+      call assert_true(b1 isnot b2)
+  END
+  call CheckLegacyAndVim9Success(lines)
 
-  call assert_fails('let x = b1 > b2')
-  call assert_fails('let x = b1 < b2')
-  call assert_fails('let x = b1 - b2')
-  call assert_fails('let x = b1 / b2')
-  call assert_fails('let x = b1 * b2')
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      echo b1 == 9
+  END
+  call CheckLegacyAndVim9Failure(lines, ['E977:', 'E1072', 'E1072'])
+
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      echo b1 != 9
+  END
+  call CheckLegacyAndVim9Failure(lines, ['E977:', 'E1072', 'E1072'])
+
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      VAR b2 = 0z1100
+      VAR x = b1 > b2
+  END
+  call CheckLegacyAndVim9Failure(lines, ['E978:', 'E1072:', 'E1072:'])
+
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      VAR b2 = 0z1100
+      VAR x = b1 < b2
+  END
+  call CheckLegacyAndVim9Failure(lines, ['E978:', 'E1072:', 'E1072:'])
+
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      VAR b2 = 0z1100
+      VAR x = b1 - b2
+  END
+  call CheckLegacyAndVim9Failure(lines, ['E974:', 'E1036:', 'E974:'])
+
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      VAR b2 = 0z1100
+      VAR x = b1 / b2
+  END
+  call CheckLegacyAndVim9Failure(lines, ['E974:', 'E1036:', 'E974:'])
+
+  let lines =<< trim END
+      VAR b1 = 0z0011
+      VAR b2 = 0z1100
+      VAR x = b1 * b2
+  END
+  call CheckLegacyAndVim9Failure(lines, ['E974:', 'E1036:', 'E974:'])
 endfunc
 
-" test for range assign
-func Test_blob_range_assign()
-  let b = 0z00
-  let b[1] = 0x11
-  let b[2] = 0x22
-  call assert_equal(0z001122, b)
-  call assert_fails('let b[4] = 0x33', 'E979:')
+func Test_blob_index_assign()
+  let lines =<< trim END
+      VAR b = 0z00
+      LET b[1] = 0x11
+      LET b[2] = 0x22
+      call assert_equal(0z001122, b)
+  END
+  call CheckLegacyAndVim9Success(lines)
+
+  let lines =<< trim END
+      VAR b = 0z00
+      LET b[2] = 0x33
+  END
+  call CheckLegacyAndVim9Failure(lines, 'E979:')
+
+  let lines =<< trim END
+      VAR b = 0z00
+      LET b[-2] = 0x33
+  END
+  call CheckLegacyAndVim9Failure(lines, 'E979:')
 endfunc
 
 func Test_blob_for_loop()
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index 3ea2ad9..e6b3751 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -246,6 +246,8 @@
   locallist[0] = 123
   var localdict: dict<number> = {}
   localdict["a"] = 456
+  var localblob: blob = 0z1122
+  localblob[1] = 33
 enddef
 
 def Test_disassemble_store_member()
@@ -259,7 +261,7 @@
         '\d PUSHNR 123\_s*' ..
         '\d PUSHNR 0\_s*' ..
         '\d LOAD $0\_s*' ..
-        '\d STORELIST\_s*' ..
+        '\d STOREINDEX list\_s*' ..
         'var localdict: dict<number> = {}\_s*' ..
         '\d NEWDICT size 0\_s*' ..
         '\d SETTYPE dict<number>\_s*' ..
@@ -268,7 +270,15 @@
         '\d\+ PUSHNR 456\_s*' ..
         '\d\+ PUSHS "a"\_s*' ..
         '\d\+ LOAD $1\_s*' ..
-        '\d\+ STOREDICT\_s*' ..
+        '\d\+ STOREINDEX dict\_s*' ..
+        'var localblob: blob = 0z1122\_s*' ..
+        '\d\+ PUSHBLOB 0z1122\_s*' ..
+        '\d\+ STORE $2\_s*' ..
+        'localblob\[1\] = 33\_s*' ..
+        '\d\+ PUSHNR 33\_s*' ..
+        '\d\+ PUSHNR 1\_s*' ..
+        '\d\+ LOAD $2\_s*' ..
+        '\d\+ STOREINDEX blob\_s*' ..
         '\d\+ RETURN 0',
         res)
 enddef
@@ -291,7 +301,7 @@
         '\d PUSHNR 0\_s*' ..
         '\d LOAD $0\_s*' ..
         '\d MEMBER dd\_s*' ..
-        '\d STOREINDEX\_s*' ..
+        '\d STOREINDEX any\_s*' ..
         '\d\+ RETURN 0',
         res)
 enddef
diff --git a/src/version.c b/src/version.c
index e1f1526..17afa34 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2777,
+/**/
     2776,
 /**/
     2775,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 801f9c1..9cb7129 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -6209,14 +6209,21 @@
 	}
 	if (dest_type == VAR_DICT && may_generate_2STRING(-1, cctx) == FAIL)
 	    return FAIL;
-	if (dest_type == VAR_LIST)
+	if (dest_type == VAR_LIST || dest_type == VAR_BLOB)
 	{
-	    if (range
-		  && need_type(((type_T **)stack->ga_data)[stack->ga_len - 2],
-				 &t_number, -1, 0, cctx, FALSE, FALSE) == FAIL)
+	    type_T *type;
+
+	    if (range)
+	    {
+		type = ((type_T **)stack->ga_data)[stack->ga_len - 2];
+		if (need_type(type, &t_number,
+					    -1, 0, cctx, FALSE, FALSE) == FAIL)
 		return FAIL;
-	    if (need_type(((type_T **)stack->ga_data)[stack->ga_len - 1],
-				 &t_number, -1, 0, cctx, FALSE, FALSE) == FAIL)
+	    }
+	    type = ((type_T **)stack->ga_data)[stack->ga_len - 1];
+	    if ((dest_type != VAR_BLOB || type != &t_special)
+		    && need_type(type, &t_number,
+					    -1, 0, cctx, FALSE, FALSE) == FAIL)
 		return FAIL;
 	}
     }
diff --git a/src/vim9execute.c b/src/vim9execute.c
index abcbce0..8a98521 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2221,7 +2221,35 @@
 		    }
 		    else if (status == OK && dest_type == VAR_BLOB)
 		    {
-			// TODO
+			long	    lidx = (long)tv_idx->vval.v_number;
+			blob_T	    *blob = tv_dest->vval.v_blob;
+			varnumber_T nr;
+			int	    error = FALSE;
+			int	    len;
+
+			if (blob == NULL)
+			{
+			    emsg(_(e_blob_not_set));
+			    goto on_error;
+			}
+			len = blob_len(blob);
+			if (lidx < 0 && len + lidx >= 0)
+			    // negative index is relative to the end
+			    lidx = len + lidx;
+
+			// Can add one byte at the end.
+			if (lidx < 0 || lidx > len)
+			{
+			    semsg(_(e_blobidx), lidx);
+			    goto on_error;
+			}
+			if (value_check_lock(blob->bv_lock,
+						      (char_u *)"blob", FALSE))
+			    goto on_error;
+			nr = tv_get_number_chk(tv, &error);
+			if (error)
+			    goto on_error;
+			blob_set_append(blob, lidx, nr);
 		    }
 		    else
 		    {
@@ -4415,19 +4443,8 @@
 		break;
 
 	    case ISN_STOREINDEX:
-		switch (iptr->isn_arg.vartype)
-		{
-		    case VAR_LIST:
-			    smsg("%4d STORELIST", current);
-			    break;
-		    case VAR_DICT:
-			    smsg("%4d STOREDICT", current);
-			    break;
-		    case VAR_ANY:
-			    smsg("%4d STOREINDEX", current);
-			    break;
-		    default: break;
-		}
+		smsg("%4d STOREINDEX %s", current,
+					  vartype_name(iptr->isn_arg.vartype));
 		break;
 
 	    case ISN_STORERANGE: