diff --git a/src/sage/knots/gauss_code.py b/src/sage/knots/gauss_code.py
index 9d5a816d577..560b6831bfc 100644
--- a/src/sage/knots/gauss_code.py
+++ b/src/sage/knots/gauss_code.py
@@ -1,3 +1,4 @@
+# sage.doctest: needs sage.graphs
 """
 Helper functions related to Gauss codes of knots
 
diff --git a/src/sage/knots/knot.py b/src/sage/knots/knot.py
index 3593983ed4b..c084a7679c8 100644
--- a/src/sage/knots/knot.py
+++ b/src/sage/knots/knot.py
@@ -1,3 +1,4 @@
+# sage.doctest: needs sage.graphs
 r"""
 Knots
 
diff --git a/src/sage/knots/knotinfo.py b/src/sage/knots/knotinfo.py
index d0dd236a2ca..0bd572223e3 100644
--- a/src/sage/knots/knotinfo.py
+++ b/src/sage/knots/knotinfo.py
@@ -1,3 +1,4 @@
+# sage.doctest: needs sage.graphs
 r"""
 Access to the KnotInfo database
 
diff --git a/src/sage/knots/link.py b/src/sage/knots/link.py
index 857c08544e9..865d7aebbb7 100644
--- a/src/sage/knots/link.py
+++ b/src/sage/knots/link.py
@@ -1,3 +1,4 @@
+# sage.doctest: needs sage.graphs
 r"""
 Links