diff --git a/doc/ext/support_matrix.py b/doc/ext/support_matrix.py
index 34d330e1e5..c3ab7a796f 100644
--- a/doc/ext/support_matrix.py
+++ b/doc/ext/support_matrix.py
@@ -81,8 +81,10 @@ class SupportMatrixImplementation(object):
     STATUS_COMPLETE = "complete"
     STATUS_PARTIAL = "partial"
     STATUS_MISSING = "missing"
+    STATUS_UKNOWN = "unknown"
 
-    STATUS_ALL = [STATUS_COMPLETE, STATUS_PARTIAL, STATUS_MISSING]
+    STATUS_ALL = [STATUS_COMPLETE, STATUS_PARTIAL, STATUS_MISSING,
+                  STATUS_UKNOWN]
 
     def __init__(self, status=STATUS_MISSING, notes=None):
         # One of the status constants detailing the implementation
@@ -346,12 +348,14 @@ class SupportMatrixDirective(rst.Directive):
                 impltxt.append(implref)
 
                 status = ""
-                if impl.status == "complete":
+                if impl.status == SupportMatrixImplementation.STATUS_COMPLETE:
                     status = u"\u2714"
-                elif impl.status == "missing":
+                elif impl.status == SupportMatrixImplementation.STATUS_MISSING:
                     status = u"\u2716"
-                elif impl.status == "partial":
+                elif impl.status == SupportMatrixImplementation.STATUS_PARTIAL:
                     status = u"\u2714"
+                elif impl.status == SupportMatrixImplementation.STATUS_UKNOWN:
+                    status = u"?"
 
                 implref.append(nodes.literal(
                     text=status,
diff --git a/doc/source/_static/support-matrix.css b/doc/source/_static/support-matrix.css
index 1758ea4122..4fd9fa7b66 100644
--- a/doc/source/_static/support-matrix.css
+++ b/doc/source/_static/support-matrix.css
@@ -32,6 +32,11 @@
     font-weight: normal;
 }
 
+.sp_impl_unknown {
+    color: rgb(170, 170, 170);
+    font-weight: normal;
+}
+
 .sp_impl_summary {
     font-size: 2em;
 }
\ No newline at end of file