diff --git a/dvc/command/diff.py b/dvc/command/diff.py
index 12fde9264..ca316d116 100644
--- a/dvc/command/diff.py
+++ b/dvc/command/diff.py
@@ -86,7 +86,7 @@ class CmdDiff(CmdBase):
             if not any(diff.values()):
                 return 0
 
-            if self.args.json:
+            if self.args.show_json:
                 res = json.dumps(diff)
             else:
                 res = self._format(diff, include_checksums=self.args.checksums)
@@ -136,7 +136,7 @@ def add_parser(subparsers, parent_parser):
         ),
     )
     diff_parser.add_argument(
-        "--json",
+        "--show-json",
         help="Format the output into a JSON",
         action="store_true",
         default=False,
diff --git a/scripts/completion/dvc.bash b/scripts/completion/dvc.bash
index 128a64326..b64839029 100644
--- a/scripts/completion/dvc.bash
+++ b/scripts/completion/dvc.bash
@@ -22,7 +22,7 @@ _dvc_checkout='-d --with-deps -R --recursive -f --force --relink $(compgen -G *.
 _dvc_commit='-f --force -d --with-deps -R --recursive $(compgen -G *.dvc)'
 _dvc_config='-u --unset --local --system --global'
 _dvc_destroy='-f --force'
-_dvc_diff='-t --target --json --checksums'
+_dvc_diff='-t --target --show-json --checksums'
 _dvc_fetch='-j --jobs -r --remote -a --all-branches -T --all-tags -d --with-deps -R --recursive $(compgen -G *.dvc)'
 _dvc_get_url=''
 _dvc_get='-o --out --rev --show-url'
diff --git a/scripts/completion/dvc.zsh b/scripts/completion/dvc.zsh
index be47469d5..08ed4f607 100644
--- a/scripts/completion/dvc.zsh
+++ b/scripts/completion/dvc.zsh
@@ -98,7 +98,7 @@ _dvc_destroy=(
 
 _dvc_diff=(
   {-t,--target}"[Source path to a data file or directory.]:Target files:"
-  "--json[Format the output into a JSON]"
+  "--show-json[Format the output into a JSON]"
   "--checksums[Display checksums for each entry]"
   {1,2}":Git revision (e.g. branch, tag, SHA):"
 )
diff --git a/tests/unit/command/test_diff.py b/tests/unit/command/test_diff.py
index 8454118f2..80ac06e4b 100644
--- a/tests/unit/command/test_diff.py
+++ b/tests/unit/command/test_diff.py
@@ -46,7 +46,7 @@ def test_checksums(mocker, caplog):
 
 
 def test_json(mocker, caplog):
-    args = parse_args(["diff", "--json"])
+    args = parse_args(["diff", "--show-json"])
     cmd = args.func(args)
     diff = {
         "added": [{"filename": "file", "checksum": "00000000"}],