--- a/hgext/hgmo/__init__.py
+++ b/hgext/hgmo/__init__.py
@@ -122,16 +122,26 @@ command = cmdutil.command(cmdtable)
 
 
 @templatefilters.templatefilter('mozlink')
 def mozlink(text):
     """Any text. Hyperlink to Bugzilla and other detected things."""
     return commitparser.add_hyperlinks(text)
 
 
+def stream_json(data):
+    """Convert a data structure to a generator of chunks representing JSON."""
+    # We use latin1 as the encoding because all data should be treated as
+    # byte strings. ensure_ascii will escape non-ascii values using \uxxxx.
+    # Also, use stable output and indentation to make testing easier.
+    encoder = json.JSONEncoder(indent=2, sort_keys=True, encoding='latin1',
+                               separators=(',', ': '))
+    return encoder.iterencode(data)
+
+
 def addmetadata(repo, ctx, d, onlycheap=False):
     """Add changeset metadata for hgweb templates."""
     description = encoding.fromlocal(ctx.description())
 
     d['bugs'] = []
     for bug in commitparser.parse_bugs(description):
         d['bugs'].append({
             'no': str(bug),
@@ -304,17 +314,17 @@ def mozbuildinfowebcommand(web, req, tmp
         return json.dumps({'error': 'unable to obtain moz.build info'},
                           indent=2)
     elif stderr.strip():
         repo.ui.log('moz.build evaluation output: %s\n' % stderr.strip())
 
     # Round trip to ensure we have valid JSON.
     try:
         d = json.loads(stdout)
-        return json.dumps(d, indent=2, sort_keys=True)
+        return stream_json(d)
     except Exception:
         return json.dumps({'error': 'invalid JSON returned; report this error'},
                           indent=2)
 
 
 def infowebcommand(web, req, tmpl):
     """Get information about the specified changeset(s).
 
@@ -461,20 +471,17 @@ def automationrelevancewebcommand(web, r
         visible = None
 
     data = {
         'changesets': csets,
         'visible': visible,
     }
 
     req.respond(HTTP_OK, 'application/json')
-    # We use latin1 as the encoding here because all data should be treated as
-    # byte strings. ensure_ascii will escape non-ascii values using \uxxxx.
-    return json.dumps(data, indent=2, sort_keys=True, encoding='latin1',
-                      separators=(',', ': '))
+    return stream_json(data)
 
 
 def revset_reviewer(repo, subset, x):
     """``reviewer(REVIEWER)``
 
     Changesets reviewed by a specific person.
     """
     l = revset.getargs(x, 1, 1, 'reviewer requires one argument')

--- a/hgext/hgmo/tests/test-mozbuildinfo-webcommand.t
+++ b/hgext/hgmo/tests/test-mozbuildinfo-webcommand.t
@@ -76,31 +76,31 @@ mozbuildinfo is available via web comman
   200
   content-type: application/json
   
   {
     "aggregate": {
       "bug_component_counts": [
         [
           [
-            "Product1", 
+            "Product1",
             "Component 1"
-          ], 
+          ],
           1
         ]
-      ], 
+      ],
       "recommended_bug_component": [
-        "Product1", 
+        "Product1",
         "Component 1"
       ]
-    }, 
+    },
     "files": {
       "moz.build": {
         "bug_component": [
-          "Product1", 
+          "Product1",
           "Component 1"
         ]
       }
     }
   }
 
 we can request info for specific files
 
@@ -108,37 +108,37 @@ we can request info for specific files
   200
   content-type: application/json
   
   {
     "aggregate": {
       "bug_component_counts": [
         [
           [
-            "Product1", 
+            "Product1",
             "Component 1"
-          ], 
+          ],
           2
         ]
-      ], 
+      ],
       "recommended_bug_component": [
-        "Product1", 
+        "Product1",
         "Component 1"
       ]
-    }, 
+    },
     "files": {
       "file1": {
         "bug_component": [
-          "Product1", 
+          "Product1",
           "Component 1"
         ]
-      }, 
+      },
       "file2": {
         "bug_component": [
-          "Product1", 
+          "Product1",
           "Component 1"
         ]
       }
     }
   }
 
 Errors displayed properly