diff --git a/src/functions.ts b/src/functions.ts
index 862dd28..04af7fd 100644
--- a/src/functions.ts
+++ b/src/functions.ts
@@ -11,10 +11,6 @@ import SpanContext from './span_context';
  * @return a REFERENCE_CHILD_OF reference pointing to `spanContext`
  */
 export function childOf(spanContext: SpanContext | Span): Reference {
-    // Allow the user to pass a Span instead of a SpanContext
-    if (spanContext instanceof Span) {
-        spanContext = spanContext.context();
-    }
     return new Reference(Constants.REFERENCE_CHILD_OF, spanContext);
 }
 
@@ -26,9 +22,5 @@ export function childOf(spanContext: SpanContext | Span): Reference {
  * @return a REFERENCE_FOLLOWS_FROM reference pointing to `spanContext`
  */
 export function followsFrom(spanContext: SpanContext | Span): Reference {
-    // Allow the user to pass a Span instead of a SpanContext
-    if (spanContext instanceof Span) {
-        spanContext = spanContext.context();
-    }
     return new Reference(Constants.REFERENCE_FOLLOWS_FROM, spanContext);
 }
diff --git a/src/reference.ts b/src/reference.ts
index cf87e25..30d4a92 100644
--- a/src/reference.ts
+++ b/src/reference.ts
@@ -1,6 +1,23 @@
 import Span from './span';
 import SpanContext from './span_context';
 
+const toContext = (contextOrSpan: SpanContext | Span): SpanContext => {
+    if (contextOrSpan instanceof SpanContext) {
+      return contextOrSpan;
+    }
+
+    // Second check is for cases when a Span implementation does not extend
+    // opentracing.Span class directly (like Jaeger), just implements the same interface.
+    // The only false-positive case here is a non-extending SpanContext class,
+    // which has a method called "context".
+    // But that's too much of a specification violation to take care of.
+    if (contextOrSpan instanceof Span || 'context' in contextOrSpan) {
+      return contextOrSpan.context();
+    }
+
+    return contextOrSpan;
+};
+
 /**
  * Reference pairs a reference type constant (e.g., REFERENCE_CHILD_OF or
  * REFERENCE_FOLLOWS_FROM) with the SpanContext it points to.
@@ -39,9 +56,6 @@ export default class Reference {
      */
     constructor(type: string, referencedContext: SpanContext | Span) {
         this._type = type;
-        this._referencedContext = (
-                referencedContext instanceof Span ?
-                referencedContext.context() :
-                referencedContext);
+        this._referencedContext = toContext(referencedContext);
     }
 }
diff --git a/src/test/opentracing_api.ts b/src/test/opentracing_api.ts
index ec4892b..3c99474 100644
--- a/src/test/opentracing_api.ts
+++ b/src/test/opentracing_api.ts
@@ -1,6 +1,11 @@
 
 import { expect } from 'chai';
 import * as opentracing from '../index';
+import MockContext from '../mock_tracer/mock_context';
+import MockSpan from '../mock_tracer/mock_span';
+import MockTracer from '../mock_tracer/mock_tracer';
+import Span from '../span';
+import SpanContext from '../span_context';
 
 export function opentracingAPITests(): void {
     describe('Opentracing API', () => {
@@ -85,6 +90,36 @@ export function opentracingAPITests(): void {
                 const ref = new opentracing.Reference(opentracing.REFERENCE_CHILD_OF, span.context());
                 expect(ref).to.be.an('object');
             });
+
+            it('should get context from custom extending span classes', () => {
+                const span = new MockSpan(new MockTracer());
+                const ref = new opentracing.Reference(opentracing.REFERENCE_CHILD_OF, span);
+                expect(ref.referencedContext() instanceof SpanContext).to.equal(true);
+            });
+
+            it('should get context from custom non-extending span classes', () => {
+                const ctx = new SpanContext();
+                const pseudoSpan = {
+                    context: () => ctx
+                } as Span;
+                const ref = new opentracing.Reference(opentracing.REFERENCE_CHILD_OF, pseudoSpan);
+                expect(ref.referencedContext()).to.equal(ctx);
+            });
+
+            it('should use extending contexts', () => {
+                const ctx = new MockContext({} as MockSpan);
+                const ref = new opentracing.Reference(opentracing.REFERENCE_CHILD_OF, ctx);
+                expect(ref.referencedContext()).to.equal(ctx);
+            });
+
+            it('should use non-extending contexts', () => {
+                const ctx = {
+                    toTraceId: () => '',
+                    toSpanId: () => ''
+                };
+                const ref = new opentracing.Reference(opentracing.REFERENCE_CHILD_OF, ctx);
+                expect(ref.referencedContext()).to.equal(ctx);
+            });
         });
 
         describe('BinaryCarrier', () => {