diff --git a/library/src/main/java/com/bumptech/glide/RequestBuilder.java b/library/src/main/java/com/bumptech/glide/RequestBuilder.java
index 366da0bbec..3a559a9b2a 100644
--- a/library/src/main/java/com/bumptech/glide/RequestBuilder.java
+++ b/library/src/main/java/com/bumptech/glide/RequestBuilder.java
@@ -859,6 +859,13 @@ public FutureTarget<TranscodeType> submit(int width, int height) {
    * <p>Pre-loading is useful for making sure that resources you are going to to want in the near
    * future are available quickly.
    *
+   * <p>Note - Any thumbnail request that does not complete before the primary request will be
+   * cancelled and may not be preloaded successfully. Cancellation of outstanding thumbnails after
+   * the primary request succeeds is a common behavior of all Glide requests. We do not try to
+   * prevent that behavior here. If you absolutely need all thumbnails to be preloaded individually,
+   * make separate preload() requests for each thumbnail (you can still combine them into one call
+   * when loading the image(s) into the UI in a subsequent request).
+   *
    * @param width The desired width in pixels, or {@link Target#SIZE_ORIGINAL}. This will be
    *     overridden by {@link com.bumptech.glide.request.RequestOptions#override(int, int)} if
    *     previously called.
diff --git a/library/src/main/java/com/bumptech/glide/request/target/PreloadTarget.java b/library/src/main/java/com/bumptech/glide/request/target/PreloadTarget.java
index 9521005322..6d3cb587b3 100644
--- a/library/src/main/java/com/bumptech/glide/request/target/PreloadTarget.java
+++ b/library/src/main/java/com/bumptech/glide/request/target/PreloadTarget.java
@@ -8,6 +8,7 @@
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import com.bumptech.glide.RequestManager;
+import com.bumptech.glide.request.Request;
 import com.bumptech.glide.request.transition.Transition;
 import com.bumptech.glide.util.Synthetic;
 
@@ -53,7 +54,17 @@ private PreloadTarget(RequestManager requestManager, int width, int height) {
 
   @Override
   public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
-    HANDLER.obtainMessage(MESSAGE_CLEAR, this).sendToTarget();
+    // If a thumbnail request is set and the thumbnail completes, we don't want to cancel the
+    // primary load. Instead we wait until the primary request (the one set on the target) says
+    // that it is complete.
+    // Note - Any thumbnail request that does not complete before the primary request will be
+    // cancelled and may not be preloaded successfully. Cancellation of outstanding thumbnails after
+    // the primary request succeeds is a common behavior of all Glide requests and we're not trying
+    // to override it here.
+    Request request = getRequest();
+    if (request != null && request.isComplete()) {
+      HANDLER.obtainMessage(MESSAGE_CLEAR, this).sendToTarget();
+    }
   }
 
   @Override
diff --git a/library/test/src/test/java/com/bumptech/glide/request/target/PreloadTargetTest.java b/library/test/src/test/java/com/bumptech/glide/request/target/PreloadTargetTest.java
index 6c46169510..63cacaca87 100644
--- a/library/test/src/test/java/com/bumptech/glide/request/target/PreloadTargetTest.java
+++ b/library/test/src/test/java/com/bumptech/glide/request/target/PreloadTargetTest.java
@@ -2,9 +2,12 @@
 
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
-import static org.robolectric.annotation.LooperMode.Mode.LEGACY;
+import static org.mockito.Mockito.when;
+import static org.robolectric.Shadows.shadowOf;
 
+import android.os.Looper;
 import com.bumptech.glide.RequestManager;
 import com.bumptech.glide.request.Request;
 import org.junit.Before;
@@ -14,9 +17,7 @@
 import org.mockito.MockitoAnnotations;
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.annotation.Config;
-import org.robolectric.annotation.LooperMode;
 
-@LooperMode(LEGACY)
 @RunWith(RobolectricTestRunner.class)
 @Config(sdk = 18)
 public class PreloadTargetTest {
@@ -26,6 +27,7 @@ public class PreloadTargetTest {
   @Before
   public void setUp() {
     MockitoAnnotations.initMocks(this);
+    shadowOf(Looper.getMainLooper()).pause();
   }
 
   @Test
@@ -39,13 +41,58 @@ public void testCallsSizeReadyWithGivenDimensions() {
     verify(cb).onSizeReady(eq(width), eq(height));
   }
 
+  // This isn't really supposed to happen, but just to double check...
   @Test
-  public void testClearsTargetInOnResourceReady() {
+  public void onResourceReady_withNullRequest_doesNotClearTarget() {
+    PreloadTarget<Object> target = PreloadTarget.obtain(requestManager, 100, 100);
+    target.setRequest(null);
+
+    callOnResourceReadyAndRunUiRunnables(target);
+
+    verify(requestManager, never()).clear(target);
+  }
+
+  @Test
+  public void onResourceReady_withNotYetCompleteRequest_doesNotClearTarget() {
+    Request request = mock(Request.class);
+    when(request.isComplete()).thenReturn(false);
+
+    PreloadTarget<Object> target = PreloadTarget.obtain(requestManager, 100, 100);
+    target.setRequest(request);
+
+    callOnResourceReadyAndRunUiRunnables(target);
+
+    verify(requestManager, never()).clear(target);
+  }
+
+  @Test
+  public void onResourceReady_withCompleteRequest_postsToClearTarget() {
+    Request request = mock(Request.class);
+    when(request.isComplete()).thenReturn(true);
+
+    PreloadTarget<Object> target = PreloadTarget.obtain(requestManager, 100, 100);
+    target.setRequest(request);
+
+    callOnResourceReadyAndRunUiRunnables(target);
+
+    verify(requestManager).clear(target);
+  }
+
+  @Test
+  public void onResourceReady_withCompleteRequest_doesNotImmediatelyClearTarget() {
     Request request = mock(Request.class);
+    when(request.isComplete()).thenReturn(true);
+
     PreloadTarget<Object> target = PreloadTarget.obtain(requestManager, 100, 100);
     target.setRequest(request);
-    target.onResourceReady(new Object(), null);
 
-    verify(requestManager).clear(eq(target));
+    target.onResourceReady(new Object(), /* transition= */ null);
+
+    verify(requestManager, never()).clear(target);
+  }
+
+  private void callOnResourceReadyAndRunUiRunnables(Target<Object> target) {
+    target.onResourceReady(new Object(), /* transition= */ null);
+    shadowOf(Looper.getMainLooper()).idle();
   }
 }