diff --git a/sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java b/sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java
index 76717ad6b9f5..9295981744d5 100644
--- a/sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java
+++ b/sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java
@@ -23,6 +23,7 @@
 import static org.apache.beam.sdk.transforms.Contextful.fn;
 
 import com.google.auto.value.AutoValue;
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.MoreObjects;
 import com.google.common.collect.Lists;
 import java.io.IOException;
@@ -1147,6 +1148,52 @@ public Write<DestinationT, UserT> withIgnoreWindowing() {
       return toBuilder().setIgnoreWindowing(true).build();
     }
 
+    @VisibleForTesting
+    Contextful<Fn<DestinationT, FileNaming>> resolveFileNamingFn() {
+      if (getDynamic()) {
+        checkArgument(
+                getConstantFileNaming() == null,
+                "when using writeDynamic(), must use versions of .withNaming() "
+                        + "that take functions from DestinationT");
+        checkArgument(getFilenamePrefix() == null, ".withPrefix() requires write()");
+        checkArgument(getFilenameSuffix() == null, ".withSuffix() requires write()");
+        checkArgument(
+                getFileNamingFn() != null,
+                "when using writeDynamic(), must specify "
+                        + ".withNaming() taking a function form DestinationT");
+        return fn(
+                        (element, c) -> {
+                          FileNaming naming = getFileNamingFn().getClosure().apply(element, c);
+                          return getOutputDirectory() == null
+                                  ? naming
+                                  : relativeFileNaming(getOutputDirectory(), naming);
+                        },
+                        getFileNamingFn().getRequirements());
+      } else {
+        checkArgument(getFileNamingFn() == null,
+                ".withNaming() taking a function from DestinationT requires writeDynamic()");
+        FileNaming constantFileNaming;
+        if (getConstantFileNaming() == null) {
+          constantFileNaming = defaultNaming(
+                  MoreObjects.firstNonNull(
+                          getFilenamePrefix(), StaticValueProvider.of("output")),
+                  MoreObjects.firstNonNull(getFilenameSuffix(), StaticValueProvider.of("")));
+        } else {
+          checkArgument(
+                  getFilenamePrefix() == null,
+                  ".to(FileNaming) is incompatible with .withSuffix()");
+          checkArgument(
+                  getFilenameSuffix() == null,
+                  ".to(FileNaming) is incompatible with .withPrefix()");
+          constantFileNaming = getConstantFileNaming();
+        }
+        if (getOutputDirectory() != null) {
+          constantFileNaming = relativeFileNaming(getOutputDirectory(), constantFileNaming);
+        }
+        return fn(SerializableFunctions.<DestinationT, FileNaming>constant(constantFileNaming));
+      }
+    }
+
     @Override
     public WriteFilesResult<DestinationT> expand(PCollection<UserT> input) {
       Write.Builder<DestinationT, UserT> resolvedSpec = new AutoValue_FileIO_Write.Builder<>();
@@ -1172,52 +1219,7 @@ public WriteFilesResult<DestinationT> expand(PCollection<UserT> input) {
         resolvedSpec.setDestinationCoder((Coder) VoidCoder.of());
       }
 
-      // Resolve fileNamingFn
-      Contextful<Fn<DestinationT, FileNaming>> fileNamingFn;
-      if (getDynamic()) {
-        checkArgument(
-            getConstantFileNaming() == null,
-            "when using writeDynamic(), must use versions of .withNaming() "
-                + "that take functions from DestinationT");
-        checkArgument(getFilenamePrefix() == null, ".withPrefix() requires write()");
-        checkArgument(getFilenameSuffix() == null, ".withSuffix() requires write()");
-        checkArgument(
-            getFileNamingFn() != null,
-            "when using writeDynamic(), must specify "
-                + ".withNaming() taking a function form DestinationT");
-        fileNamingFn =
-            Contextful.fn(
-                (element, c) -> {
-                  FileNaming naming = getFileNamingFn().getClosure().apply(element, c);
-                  return getOutputDirectory() == null
-                      ? naming
-                      : relativeFileNaming(getOutputDirectory(), naming);
-                },
-                getFileNamingFn().getRequirements());
-      } else {
-        checkArgument(getFileNamingFn() == null,
-            ".withNaming() taking a function from DestinationT requires writeDynamic()");
-        FileNaming constantFileNaming;
-        if (getConstantFileNaming() == null) {
-          constantFileNaming = defaultNaming(
-              MoreObjects.firstNonNull(
-                  getFilenamePrefix(), StaticValueProvider.of("output")),
-              MoreObjects.firstNonNull(getFilenameSuffix(), StaticValueProvider.of("")));
-          if (getOutputDirectory() != null) {
-            constantFileNaming = relativeFileNaming(getOutputDirectory(), constantFileNaming);
-          }
-        } else {
-          checkArgument(
-              getFilenamePrefix() == null, ".to(FileNaming) is incompatible with .withSuffix()");
-          checkArgument(
-              getFilenameSuffix() == null, ".to(FileNaming) is incompatible with .withPrefix()");
-          constantFileNaming = getConstantFileNaming();
-        }
-        fileNamingFn =
-            fn(SerializableFunctions.<DestinationT, FileNaming>constant(constantFileNaming));
-      }
-
-      resolvedSpec.setFileNamingFn(fileNamingFn);
+      resolvedSpec.setFileNamingFn(resolveFileNamingFn());
       resolvedSpec.setEmptyWindowDestination(getEmptyWindowDestination());
       if (getTempDirectory() == null) {
         checkArgument(
diff --git a/sdks/java/core/src/test/java/org/apache/beam/sdk/io/FileIOTest.java b/sdks/java/core/src/test/java/org/apache/beam/sdk/io/FileIOTest.java
index 608fd0a8b1c6..15989d622a87 100644
--- a/sdks/java/core/src/test/java/org/apache/beam/sdk/io/FileIOTest.java
+++ b/sdks/java/core/src/test/java/org/apache/beam/sdk/io/FileIOTest.java
@@ -17,6 +17,7 @@
  */
 package org.apache.beam.sdk.io;
 
+import static org.apache.beam.sdk.io.fs.ResolveOptions.StandardResolveOptions.RESOLVE_FILE;
 import static org.hamcrest.Matchers.isA;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -42,6 +43,8 @@
 import org.apache.beam.sdk.testing.UsesSplittableParDo;
 import org.apache.beam.sdk.transforms.Create;
 import org.apache.beam.sdk.transforms.Watch;
+import org.apache.beam.sdk.transforms.windowing.GlobalWindow;
+import org.apache.beam.sdk.transforms.windowing.PaneInfo;
 import org.apache.beam.sdk.values.PCollection;
 import org.joda.time.Duration;
 import org.junit.Rule;
@@ -301,4 +304,106 @@ private static MatchResult.Metadata metadata(Path path, int size) {
         .setSizeBytes(size)
         .build();
   }
+
+  @Test
+  public void testFilenameFnResolution() throws Exception {
+    FileIO.Write.FileNaming testFileNaming = FileIO.writeDynamic()
+            .to("test")
+            .withNaming(o -> (window, pane, numShards, shardIndex, compression) -> "foo")
+            .resolveFileNamingFn()
+            .getClosure()
+            .apply(null, null);
+
+    assertEquals(
+            "Filenames should be resolved within a relative directory if '.to' is invoked",
+            FileSystems.matchNewResource("test", true)
+                    .resolve("foo", RESOLVE_FILE)
+                    .toString(),
+            testFileNaming.getFilename(null, null, 0, 0, null)
+    );
+
+    testFileNaming = FileIO.write()
+            .to("test")
+            .withNaming((window, pane, numShards, shardIndex, compression) -> "foo")
+            .resolveFileNamingFn()
+            .getClosure()
+            .apply(null, null);
+
+    assertEquals(
+            "Filenames should be resolved within a relative directory if '.to' is invoked",
+            FileSystems.matchNewResource("test", true)
+                    .resolve("foo", RESOLVE_FILE)
+                    .toString(),
+            testFileNaming.getFilename(null, null, 0, 0, null)
+    );
+
+    testFileNaming = FileIO.writeDynamic()
+            .withNaming(o -> (window, pane, numShards, shardIndex, compression) -> "foo")
+            .resolveFileNamingFn()
+            .getClosure()
+            .apply(null, null);
+
+    assertEquals(
+            "Filenames should be resolved as the direct result of the filenaming function if '.to' "
+                     + "is not invoked",
+            "foo",
+            testFileNaming.getFilename(null, null, 0, 0, null)
+    );
+
+    testFileNaming = FileIO.write()
+            .withNaming((window, pane, numShards, shardIndex, compression) -> "foo")
+            .resolveFileNamingFn()
+            .getClosure()
+            .apply(null, null);
+
+    assertEquals(
+            "Filenames should be resolved as the direct result of the filenaming function if '.to' "
+                     + "is not invoked",
+            "foo",
+            testFileNaming.getFilename(null, null, 0, 0, null)
+    );
+
+    testFileNaming = FileIO.write()
+            .resolveFileNamingFn()
+            .getClosure()
+            .apply(null, null);
+
+    assertEquals(
+            "Default to the defaultNaming if a filenaming isn't provided for a non-dynamic write",
+            "output-00000-of-00000",
+            testFileNaming.getFilename(GlobalWindow.INSTANCE, PaneInfo.ON_TIME_AND_ONLY_FIRING, 0,
+                    0, Compression.UNCOMPRESSED)
+    );
+
+    testFileNaming = FileIO.write()
+            .withPrefix("foo")
+            .withSuffix(".bar")
+            .resolveFileNamingFn()
+            .getClosure()
+            .apply(null, null);
+
+    assertEquals(
+            "Default Naming should take prefix and suffix into account if provided",
+            "foo-00000-of-00000.bar",
+            testFileNaming.getFilename(GlobalWindow.INSTANCE, PaneInfo.ON_TIME_AND_ONLY_FIRING, 0,
+                    0, Compression.UNCOMPRESSED)
+    );
+
+    testFileNaming = FileIO.write()
+            .to("test")
+            .resolveFileNamingFn()
+            .getClosure()
+            .apply(null, null);
+
+
+    assertEquals(
+            "Filenames should be resolved within a relative directory if '.to' is invoked, "
+                     + "even with default naming",
+            FileSystems.matchNewResource("test", true)
+                    .resolve("output-00000-of-00000", RESOLVE_FILE)
+                    .toString(),
+            testFileNaming.getFilename(GlobalWindow.INSTANCE, PaneInfo.ON_TIME_AND_ONLY_FIRING, 0,
+                    0, Compression.UNCOMPRESSED)
+    );
+  }
 }