diff --git a/spec/operators/throttle-spec.ts b/spec/operators/throttle-spec.ts
index e4d9f0e44f..a854abdc95 100644
--- a/spec/operators/throttle-spec.ts
+++ b/spec/operators/throttle-spec.ts
@@ -8,7 +8,7 @@ describe('throttle operator', () =>  {
   it('should immediately emit the first value in each time window', () =>  {
     const e1 =   hot('-a-xy-----b--x--cxxx-|');
     const e1subs =   '^                    !';
-    const e2 =  cold( '----|                ');
+    const e2 =  cold( '----x                ');
     const e2subs =  [' ^   !                ',
                    '          ^   !       ',
                    '                ^   ! '];
@@ -24,7 +24,7 @@ describe('throttle operator', () =>  {
   it('should simply mirror the source if values are not emitted often enough', () =>  {
     const e1 =   hot('-a--------b-----c----|');
     const e1subs =   '^                    !';
-    const e2 =  cold( '----|                ');
+    const e2 =  cold( '----x                ');
     const e2subs =  [' ^   !                ',
                    '          ^   !       ',
                    '                ^   ! '];
@@ -57,7 +57,7 @@ describe('throttle operator', () =>  {
     const e1 =   hot('-a-x-y-z-xyz-x-y-z----b--x-x-|');
     const unsub =    '              !               ';
     const e1subs =   '^             !               ';
-    const e2 =  cold( '------------------|          ');
+    const e2 =  cold( '------------------x          ');
     const e2subs =   ' ^            !               ';
     const expected = '-a-------------               ';
 
@@ -71,7 +71,7 @@ describe('throttle operator', () =>  {
   it('should not break unsubscription chains when result is unsubscribed explicitly', () =>  {
     const e1 =   hot('-a-x-y-z-xyz-x-y-z----b--x-x-|');
     const e1subs =   '^             !               ';
-    const e2 =  cold( '------------------|          ');
+    const e2 =  cold( '------------------x          ');
     const e2subs =   ' ^            !               ';
     const expected = '-a-------------               ';
     const unsub =    '              !               ';
@@ -90,7 +90,7 @@ describe('throttle operator', () =>  {
   it('should handle a busy producer emitting a regular repeating sequence', () =>  {
     const e1 =   hot('abcdefabcdefabcdefabcdefa|');
     const e1subs =   '^                        !';
-    const e2 =  cold('-----|                    ');
+    const e2 =  cold('-----x                    ');
     const e2subs =  ['^    !                    ',
                    '      ^    !              ',
                    '            ^    !        ',
@@ -105,7 +105,19 @@ describe('throttle operator', () =>  {
     expectSubscriptions(e2.subscriptions).toBe(e2subs);
   });
 
-  it('should mirror source if durations are always empty', () =>  {
+  it('should mirror source if durations are immediate', () =>  {
+    const e1 =   hot('abcdefabcdefabcdefabcdefa|');
+    const e1subs =   '^                        !';
+    const e2 =  cold('x');
+    const expected = 'abcdefabcdefabcdefabcdefa|';
+
+    const result = e1.pipe(throttle(() =>  e2));
+
+    expectObservable(result).toBe(expected);
+    expectSubscriptions(e1.subscriptions).toBe(e1subs);
+  });
+
+  it('should mirror source if durations are empty', () =>  {
     const e1 =   hot('abcdefabcdefabcdefabcdefa|');
     const e1subs =   '^                        !';
     const e2 =  cold('|');
@@ -162,11 +174,11 @@ describe('throttle operator', () =>  {
   it('should throttle using durations of constying lengths', () =>  {
     const e1 =   hot('abcdefabcdabcdefghabca|   ');
     const e1subs =   '^                     !   ';
-    const e2 = [cold('-----|                    '),
-              cold(      '---|                '),
-              cold(          '-------|        '),
-              cold(                  '--|     '),
-              cold(                     '----|')];
+    const e2 = [cold('-----x                    '),
+              cold(      '---x                '),
+              cold(          '-------x        '),
+              cold(                  '--x     '),
+              cold(                     '----x')];
     const e2subs =  ['^    !                    ',
                    '      ^  !                ',
                    '          ^      !        ',
@@ -187,8 +199,8 @@ describe('throttle operator', () =>  {
   it('should propagate error from duration Observable', () =>  {
     const e1 =   hot('abcdefabcdabcdefghabca|   ');
     const e1subs =   '^                !        ';
-    const e2 = [cold('-----|                    '),
-              cold(      '---|                '),
+    const e2 = [cold('-----x                    '),
+              cold(      '---x                '),
               cold(          '-------#        ')];
     const e2subs =  ['^    !                    ',
                    '      ^  !                ',
@@ -208,7 +220,7 @@ describe('throttle operator', () =>  {
   it('should propagate error thrown from durationSelector function', () =>  {
     const s1 = hot('--^--x--x--x--x--x--x--e--x--x--x--|');
     const s1Subs =   '^                    !';
-    const n1 = cold( '----|');
+    const n1 = cold( '----x');
     const n1Subs =  ['   ^   !                          ',
                      '         ^   !                    ',
                      '               ^   !              '];
@@ -332,7 +344,7 @@ describe('throttle operator', () =>  {
     it('should immediately emit the first value in each time window', () =>  {
       const e1 =   hot('-a-xy-----b--x--cxxx------|');
       const e1subs =   '^                         !';
-      const e2 =  cold( '----|                     ');
+      const e2 =  cold( '----x                     ');
       const e2subs =  [' ^   !                     ',
                        '     ^   !                 ',
                        '          ^   !            ',
@@ -351,7 +363,7 @@ describe('throttle operator', () =>  {
     it('should work for individual values', () => {
       const s1 = hot('-^-x------------------|');
       const s1Subs =  '^                    !';
-      const n1 = cold(  '------------------------|');
+      const n1 = cold(  '------------------------x');
       const n1Subs = ['  ^                  !'];
       const exp =     '--x------------------|';
 
@@ -364,7 +376,7 @@ describe('throttle operator', () =>  {
     it('should emit trailing value after throttle duration when source completes', () =>  {
       const e1 =   hot('-a--------xy|  ');
       const e1subs =   '^           !  ';
-      const e2 =  cold( '----|         ');
+      const e2 =  cold( '----x         ');
       const e2subs =  [' ^   !         ',
                        '          ^   !'];
       const expected = '-a--------x---(y|)';
@@ -381,7 +393,7 @@ describe('throttle operator', () =>  {
     it('should immediately emit the first value in each time window', () =>  {
       const e1 =   hot('-a-xy-----b--x--cxxx------|');
       const e1subs =   '^                         !';
-      const e2 =  cold( '----|                     ');
+      const e2 =  cold( '----x                     ');
       const e2subs =  [' ^   !                     ',
                        '     ^   !                 ',
                        '          ^   !            ',
@@ -400,7 +412,7 @@ describe('throttle operator', () =>  {
     it('should work for individual values', () => {
       const s1 = hot('-^-x------------------|');
       const s1Subs =  '^                    !';
-      const n1 = cold(  '------------------------|');
+      const n1 = cold(  '------------------------x');
       const n1Subs = ['  ^                  !'];
       const exp =     '--x------------------|';
 
@@ -410,10 +422,10 @@ describe('throttle operator', () =>  {
       expectSubscriptions(n1.subscriptions).toBe(n1Subs);
     });
 
-    it('should wait for trailing throttle to complete before completing, even if source completes', () => {
+    it('should wait for trailing throttle before completing, even if source completes', () => {
       const source = hot( '-^--x--------y---------|');
       const sourceSubs =   '^                     !';
-      const duration = cold(  '------------------------|');
+      const duration = cold(  '------------------------x');
       const durationSubs = '   ^                       !';
       const exp =          '---x-----------------------(y|)';
 
@@ -426,7 +438,7 @@ describe('throttle operator', () =>  {
     it('should emit trailing value after throttle duration when source completes', () =>  {
       const e1 =   hot('-a--------x|   ');
       const e1subs =   '^          !   ';
-      const e2 =  cold( '----|         ');
+      const e2 =  cold( '----x         ');
       const e2subs =  [' ^   !         ',
                        '     ^   !     ',
                        '          ^   !'];
@@ -442,7 +454,7 @@ describe('throttle operator', () =>  {
     it('should emit the last trailing value after throttle duration when source completes', () =>  {
       const e1 =   hot('-a--------xy|  ');
       const e1subs =   '^           !  ';
-      const e2 =  cold( '----|         ');
+      const e2 =  cold( '----x         ');
       const e2subs =  [' ^   !         ',
                        '     ^   !     ',
                        '          ^   !'];
@@ -458,7 +470,7 @@ describe('throttle operator', () =>  {
     it('should complete when source completes if no value is available', () =>  {
       const e1 =   hot('-a-----|');
       const e1subs =   '^      !';
-      const e2 =  cold( '----| ');
+      const e2 =  cold( '----x ');
       const e2subs =  [' ^   ! ',
                        '     ^ !'];
       const expected = '-----a-|';
diff --git a/src/internal/operators/throttle.ts b/src/internal/operators/throttle.ts
index 9dff66248e..d7c48c848d 100644
--- a/src/internal/operators/throttle.ts
+++ b/src/internal/operators/throttle.ts
@@ -32,7 +32,7 @@ export const defaultThrottleConfig: ThrottleConfig = {
  * value arrives, it is forwarded to the output Observable, and then the timer
  * is enabled by calling the `durationSelector` function with the source value,
  * which returns the "duration" Observable. When the duration Observable emits a
- * value or completes, the timer is disabled, and this process repeats for the
+ * value, the timer is disabled, and this process repeats for the
  * next source value.
  *
  * ## Example
@@ -70,7 +70,7 @@ export function throttle<T>(
     let throttled: Subscription | null = null;
     let isComplete = false;
 
-    const throttlingDone = () => {
+    const endThrottling = () => {
       throttled?.unsubscribe();
       throttled = null;
       if (trailing) {
@@ -79,9 +79,14 @@ export function throttle<T>(
       }
     };
 
+    const cleanupThrottling = () => {
+      throttled = null;
+      isComplete && subscriber.complete();
+    };
+
     const startThrottle = (value: T) =>
       (throttled = innerFrom(durationSelector(value)).subscribe(
-        new OperatorSubscriber(subscriber, throttlingDone, undefined, throttlingDone)
+        new OperatorSubscriber(subscriber, endThrottling, undefined, cleanupThrottling)
       ));
 
     const send = () => {