diff --git a/src/errors.h b/src/errors.h
index 8ddf441..4d8456f 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -284,4 +284,6 @@
 	INIT(= N_("E1129: Throw with empty string"));
 EXTERN char e_cannot_add_to_null_list[]
 	INIT(= N_("E1130: Cannot add to null list"));
+EXTERN char e_cannot_add_to_null_blob[]
+	INIT(= N_("E1131: Cannot add to null blob"));
 #endif
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index fe1ce66..97797bc 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -301,6 +301,34 @@
         res)
 enddef
 
+def s:BlobAdd()
+  var b: blob = 0z
+  add(b, 123)
+  add(b, g:aNumber)
+enddef
+
+def Test_disassemble_blob_add()
+  var res = execute('disass s:BlobAdd')
+  assert_match('<SNR>\d*_BlobAdd\_s*' ..
+        'var b: blob = 0z\_s*' ..
+        '\d PUSHBLOB 0z\_s*' ..
+        '\d STORE $0\_s*' ..
+        'add(b, 123)\_s*' ..
+        '\d LOAD $0\_s*' ..
+        '\d PUSHNR 123\_s*' ..
+        '\d BLOBAPPEND\_s*' ..
+        '\d DROP\_s*' ..
+        'add(b, g:aNumber)\_s*' ..
+        '\d LOAD $0\_s*' ..
+        '\d\+ LOADG g:aNumber\_s*' ..
+        '\d\+ CHECKTYPE number stack\[-1\]\_s*' ..
+        '\d\+ BLOBAPPEND\_s*' ..
+        '\d\+ DROP\_s*' ..
+        '\d\+ PUSHNR 0\_s*' ..
+        '\d\+ RETURN',
+        res)
+enddef
+
 def s:ScriptFuncUnlet()
   g:somevar = "value"
   unlet g:somevar
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 4af136c..e8072d3 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1791,9 +1791,25 @@
 enddef
 
 def Test_blob_add()
-  var b: blob = 0z12
-  add(b, 0x34)
-  assert_equal(0z1234, b)
+  var b1: blob = 0z12
+  add(b1, 0x34)
+  assert_equal(0z1234, b1)
+
+  var b2: blob # defaults to empty blob
+  add(b2, 0x67)
+  assert_equal(0z67, b2)
+
+  var lines =<< trim END
+      var b: blob
+      add(b, "x")
+  END
+  CheckDefFailure(lines, 'E1012:', 2)
+
+  lines =<< trim END
+      var b: blob = test_null_blob()
+      add(b, 123)
+  END
+  CheckDefExecFailure(lines, 'E1131:', 2)
 enddef
 
 def SID(): number
diff --git a/src/version.c b/src/version.c
index 1b60ebd..97a3b71 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1867,
+/**/
     1866,
 /**/
     1865,
diff --git a/src/vim9.h b/src/vim9.h
index 4cece6d..68b9bfa 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -126,6 +126,7 @@
     ISN_ANYINDEX,   // [expr] runtime index
     ISN_ANYSLICE,   // [expr:expr] runtime slice
     ISN_SLICE,	    // drop isn_arg.number items from start of list
+    ISN_BLOBAPPEND, // append to a blob, like add()
     ISN_GETITEM,    // push list item, isn_arg.number is the index
     ISN_MEMBER,	    // dict[member]
     ISN_STRINGMEMBER, // dict.member using isn_arg.string
diff --git a/src/vim9compile.c b/src/vim9compile.c
index bb4807e..d9908d3 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1521,6 +1521,28 @@
 }
 
 /*
+ * Generate an ISN_BLOBAPPEND instruction.  Works like add().
+ * Argument count is already checked.
+ */
+    static int
+generate_BLOBAPPEND(cctx_T *cctx)
+{
+    garray_T	*stack = &cctx->ctx_type_stack;
+    type_T	*item_type;
+
+    // Caller already checked that blob_type is a blob.
+    item_type = ((type_T **)stack->ga_data)[stack->ga_len - 1];
+    if (need_type(item_type, &t_number, -1, cctx, FALSE, FALSE) == FAIL)
+	return FAIL;
+
+    if (generate_instr(cctx, ISN_BLOBAPPEND) == NULL)
+	return FAIL;
+
+    --stack->ga_len;	    // drop the argument
+    return OK;
+}
+
+/*
  * Generate an ISN_DCALL or ISN_UCALL instruction.
  * Return FAIL if the number of arguments is wrong.
  */
@@ -2570,13 +2592,18 @@
 		type_T	    *type = ((type_T **)stack->ga_data)[
 							    stack->ga_len - 2];
 
-		// TODO: also check for VAR_BLOB
 		if (type->tt_type == VAR_LIST)
 		{
 		    // inline "add(list, item)" so that the type can be checked
 		    res = generate_LISTAPPEND(cctx);
 		    idx = -1;
 		}
+		else if (type->tt_type == VAR_BLOB)
+		{
+		    // inline "add(blob, nr)" so that the type can be checked
+		    res = generate_BLOBAPPEND(cctx);
+		    idx = -1;
+		}
 	    }
 
 	    if (idx >= 0)
@@ -5421,7 +5448,7 @@
 			generate_PUSHS(cctx, NULL);
 			break;
 		    case VAR_BLOB:
-			generate_PUSHBLOB(cctx, NULL);
+			generate_PUSHBLOB(cctx, blob_alloc());
 			break;
 		    case VAR_FUNC:
 			generate_PUSHFUNC(cctx, NULL, &t_func_void);
@@ -7675,6 +7702,7 @@
 	case ISN_ANYINDEX:
 	case ISN_ANYSLICE:
 	case ISN_BCALL:
+	case ISN_BLOBAPPEND:
 	case ISN_CATCH:
 	case ISN_CHECKLEN:
 	case ISN_CHECKNR:
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 031761d..7a5871a 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2312,6 +2312,29 @@
 		}
 		break;
 
+	    case ISN_BLOBAPPEND:
+		{
+		    typval_T	*tv1 = STACK_TV_BOT(-2);
+		    typval_T	*tv2 = STACK_TV_BOT(-1);
+		    blob_T	*b = tv1->vval.v_blob;
+		    int		error = FALSE;
+		    varnumber_T n;
+
+		    // add a number to a blob
+		    if (b == NULL)
+		    {
+			SOURCING_LNUM = iptr->isn_lnum;
+			emsg(_(e_cannot_add_to_null_blob));
+			goto on_error;
+		    }
+		    n = tv_get_number_chk(tv2, &error);
+		    if (error)
+			goto on_error;
+		    ga_append(&b->bv_ga, (int)n);
+		    --ectx.ec_stack.ga_len;
+		}
+		break;
+
 	    // Computation with two arguments of unknown type
 	    case ISN_OPANY:
 		{
@@ -3432,6 +3455,7 @@
 	    case ISN_STRINDEX: smsg("%4d STRINDEX", current); break;
 	    case ISN_STRSLICE: smsg("%4d STRSLICE", current); break;
 	    case ISN_LISTAPPEND: smsg("%4d LISTAPPEND", current); break;
+	    case ISN_BLOBAPPEND: smsg("%4d BLOBAPPEND", current); break;
 	    case ISN_LISTINDEX: smsg("%4d LISTINDEX", current); break;
 	    case ISN_LISTSLICE: smsg("%4d LISTSLICE", current); break;
 	    case ISN_ANYINDEX: smsg("%4d ANYINDEX", current); break;