diff --git a/git_upstream/lib/drop.py b/git_upstream/lib/drop.py
index 7a7aca4..99a2b1f 100644
--- a/git_upstream/lib/drop.py
+++ b/git_upstream/lib/drop.py
@@ -69,7 +69,7 @@ class Drop(LogDedentMixin, GitMixin):
             self._author = author
 
         # test that we can use this git repo
-        if not self.is_detached():
+        if self.is_detached():
             raise DropError("In 'detached HEAD' state")
 
         # To Do: check if it possible and useful.
diff --git a/git_upstream/lib/importupstream.py b/git_upstream/lib/importupstream.py
index ed76f73..dc0772e 100644
--- a/git_upstream/lib/importupstream.py
+++ b/git_upstream/lib/importupstream.py
@@ -48,7 +48,7 @@ class ImportUpstream(LogDedentMixin, GitMixin):
         super(ImportUpstream, self).__init__(*args, **kwargs)
 
         # test that we can use this git repo
-        if not self.is_detached():
+        if self.is_detached():
             raise ImportUpstreamError("In 'detached HEAD' state")
 
         if self.repo.bare:
diff --git a/git_upstream/lib/supersede.py b/git_upstream/lib/supersede.py
index aa10ef6..423d32c 100644
--- a/git_upstream/lib/supersede.py
+++ b/git_upstream/lib/supersede.py
@@ -62,7 +62,7 @@ class Supersede(LogDedentMixin, GitMixin):
             raise SupersedeError("Commit should be provided")
 
         # test that we can use this git repo
-        if not self.is_detached():
+        if self.is_detached():
             raise SupersedeError("In 'detached HEAD' state")
 
         # To Do: check if it possible and useful.
diff --git a/git_upstream/lib/utils.py b/git_upstream/lib/utils.py
index b370063..ae34dda 100644
--- a/git_upstream/lib/utils.py
+++ b/git_upstream/lib/utils.py
@@ -53,7 +53,7 @@ class GitMixin(object):
         return self.__git
 
     def is_detached(self):
-        return self.git.symbolic_ref("HEAD", q=True, with_exceptions=False)
+        return not self.git.symbolic_ref("HEAD", q=True, with_exceptions=False)
 
     def get_name(self, sha1, pattern=None):
         """