diff --git a/indexing/basic/index.pl b/indexing/basic/index.pl
index b40996d56..e13484739 100755
--- a/indexing/basic/index.pl
+++ b/indexing/basic/index.pl
@@ -47,6 +47,7 @@ if ($needs_init) {
     $db->do("CREATE TABLE blobs (" .
             "   blobref   VARCHAR(80) NOT NULL PRIMARY KEY, " .
             "   size      INT NULL, " .
+            "   headbytes VARCHAR(1024) NULL, ".
             "   mimetype  VARCHAR(30) NULL)");
 }
 
@@ -61,10 +62,11 @@ my $json = JSON::Any->new;
 $ua->credentials($hostport, "camlistored", "user", $netrc_mach->password);
 
 print "Iterating over blobs.\n";
-my $n_blobs = learn_blob_digests_and_sizes();
+my $n_blobs = populate_blob_digests_and_sizes();
 print "Number of blobs: $n_blobs.\n";
+populate_blob_types();
 
-sub learn_blob_digests_and_sizes {
+sub populate_blob_digests_and_sizes {
     my $after = "";
     my $n_blobs = 0;
     while (1) {
@@ -110,3 +112,58 @@ sub learn_blob_digests_and_sizes {
     }
     return $n_blobs;
 }
+
+sub populate_blob_types {
+    my $after = "";
+    my $n_blobs = 0;
+    while (1) {
+        print "Querying for un-sniffed blobs after '$after'...\n";
+        my $sth = $db->prepare("SELECT blobref, size, headbytes FROM blobs WHERE " .
+                               "mimetype IS NULL AND size IS NOT NULL AND blobref > ? LIMIT 50");
+        $sth->execute($after);
+        my $cursor_count = 0;
+        while (my ($blobref, $size, $headbytes) = $sth->fetchrow_array) {
+            $after = $blobref;
+            $cursor_count++;
+            my $need_headbytes_update = 0;
+            $headbytes = "" if defined($size) && $size == 0;
+            if (defined $headbytes) {
+                print "Unknown type for $blobref ...\n";
+            } else {
+                print "Fetching $blobref ...\n";
+                my $req = HTTP::Request->new(GET => "$scheme://$hostport/camli/$blobref");
+                $req->header("Range" => "bytes=0-1024");
+                my $res = $ua->request($req);
+                unless ($res->is_success) {
+                    die "Failure fetching head of /camli/$blobref: " . $res->status_line;
+                }
+                $headbytes = $res->content;
+                $need_headbytes_update = 1;
+                my $size = length($headbytes);
+                print "Fetching $blobref = $size byte header\n";
+            }
+            my $type = get_type_from_magic($headbytes);
+            next unless $type or $need_headbytes_update;
+            print "Type of $blobref: $type\n";
+            $db->do("UPDATE blobs SET headbytes=?, mimetype=? WHERE blobref=?", undef,
+                    $headbytes, $type, $blobref);
+        }
+        print "count: $cursor_count\n";
+        last unless $cursor_count > 0;
+    }
+}
+
+sub get_type_from_magic {
+    my $magic = shift;
+    if ($magic =~ /^{.+"camliVersion"/s) {
+        return "application/json+camli";
+    }
+    if ($magic =~ /^\xff\xd8\xff\xe1/) {
+        return "image/jpeg";
+    }
+    if ($magic =~ /^<\?xml\b.+<gpx\b/s) { # TODO: over-broad
+        return "application/gpx+xml";  # not actually registered?
+    }
+    return undef;
+}
+