diff --git a/lib/call-session.js b/lib/call-session.js
index 355e174..2bcaecb 100644
--- a/lib/call-session.js
+++ b/lib/call-session.js
@@ -505,17 +505,21 @@ class CallSession extends Emitter {
         }
         else {
           const uri = parseUri(this.req.uri);
+          /* RFC 3261 8.1.1.8: a sips Request-URI requires a sips Contact */
+          const scheme = uri.scheme === 'sips' ? 'sips' : 'sip';
           hdrs = {
             ...hdrs,
             'From': createBLegFromHeader({
               logger: this.logger,
               req: this.req,
+              scheme,
               transport: uri.params.transport,
               ...(private_network && {host: this.privateSipAddress})
             }),
             'Contact': createBLegFromHeader({
               logger: this.logger,
               req: this.req,
+              scheme,
               transport: uri.params.transport,
               ...(private_network && {host: this.privateSipAddress})
             })