diff --git a/mercurial/templatekw.py b/mercurial/templatekw.py
--- a/mercurial/templatekw.py
+++ b/mercurial/templatekw.py
@@ -559,8 +559,11 @@ def shownegrev(context, mapping):
     """Integer. The repository-local changeset negative revision number,
     which counts in the opposite direction."""
     ctx = context.resource(mapping, 'ctx')
+    rev = ctx.rev()
+    if rev is None or rev < 0:  # wdir() or nullrev?
+        return None
     repo = context.resource(mapping, 'repo')
-    return scmutil.intrev(ctx) - len(repo)
+    return rev - len(repo)
 
 @templatekeyword('node', requires={'ctx'})
 def shownode(context, mapping):
diff --git a/tests/test-template-keywords.t b/tests/test-template-keywords.t
--- a/tests/test-template-keywords.t
+++ b/tests/test-template-keywords.t
@@ -76,6 +76,12 @@ experimental:
   $ hg log -r 'wdir()' -T '{manifest}\n'
   2147483647:ffffffffffff
 
+However, for negrev, we refuse to output anything (as well as for null)
+
+  $ hg log -r 'wdir() + null' -T 'bla{negrev}nk\n'
+  blank
+  blank
+
 Changectx-derived keywords are disabled within {manifest} as {node} changes:
 
   $ hg log -r0 -T 'outer:{p1node} {manifest % "inner:{p1node}"}\n'