diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BazelFileSystemModule.java b/src/main/java/com/google/devtools/build/lib/runtime/BazelFileSystemModule.java
index db26f14..9f339d5 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BazelFileSystemModule.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BazelFileSystemModule.java
@@ -20,6 +20,7 @@
 import com.google.devtools.build.lib.util.OS;
 import com.google.devtools.build.lib.vfs.DigestHashFunction;
 import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultAlreadySetException;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import com.google.devtools.build.lib.vfs.DigestHashFunction.DigestFunctionConverter;
 import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.JavaIoFileSystem;
@@ -60,7 +61,8 @@
   }
 
   @Override
-  public FileSystem getFileSystem(OptionsParsingResult startupOptions) {
+  public FileSystem getFileSystem(OptionsParsingResult startupOptions)
+      throws DefaultHashFunctionNotSetException {
     if ("0".equals(System.getProperty("io.bazel.EnableJni"))) {
       // Ignore UnixFileSystem, to be used for bootstrapping.
       return OS.getCurrent() == OS.WINDOWS ? new WindowsFileSystem() : new JavaIoFileSystem();
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java b/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java
index f2105fd..ba47faa 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BlazeModule.java
@@ -31,6 +31,7 @@
 import com.google.devtools.build.lib.skyframe.PrecomputedValue;
 import com.google.devtools.build.lib.util.AbruptExitException;
 import com.google.devtools.build.lib.util.io.OutErr;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.OutputService;
 import com.google.devtools.build.lib.vfs.Path;
@@ -81,7 +82,8 @@
    *
    * @param startupOptions the server's startup options
    */
-  public FileSystem getFileSystem(OptionsParsingResult startupOptions) throws AbruptExitException {
+  public FileSystem getFileSystem(OptionsParsingResult startupOptions)
+      throws AbruptExitException, DefaultHashFunctionNotSetException {
     return null;
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java b/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
index 3a7e9b5..a9df409 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BlazeRuntime.java
@@ -73,6 +73,7 @@
 import com.google.devtools.build.lib.util.ProcessUtils;
 import com.google.devtools.build.lib.util.ThreadUtils;
 import com.google.devtools.build.lib.util.io.OutErr;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.JavaIoFileSystem;
 import com.google.devtools.build.lib.vfs.Path;
@@ -965,7 +966,8 @@
     }
   }
 
-  private static FileSystem defaultFileSystemImplementation() {
+  private static FileSystem defaultFileSystemImplementation()
+      throws DefaultHashFunctionNotSetException {
     if ("0".equals(System.getProperty("io.bazel.EnableJni"))) {
       // Ignore UnixFileSystem, to be used for bootstrapping.
       return OS.getCurrent() == OS.WINDOWS ? new WindowsFileSystem() : new JavaIoFileSystem();
@@ -1063,18 +1065,22 @@
     }
 
     FileSystem fs = null;
-    for (BlazeModule module : blazeModules) {
-      FileSystem moduleFs = module.getFileSystem(options);
-      if (moduleFs != null) {
-        Preconditions.checkState(fs == null, "more than one module returns a file system");
-        fs = moduleFs;
+    try {
+      for (BlazeModule module : blazeModules) {
+        FileSystem moduleFs = module.getFileSystem(options);
+        if (moduleFs != null) {
+          Preconditions.checkState(fs == null, "more than one module returns a file system");
+          fs = moduleFs;
+        }
       }
-    }
 
-    if (fs == null) {
-      fs = defaultFileSystemImplementation();
+      if (fs == null) {
+        fs = defaultFileSystemImplementation();
+      }
+    } catch (DefaultHashFunctionNotSetException e) {
+      throw new AbruptExitException(
+          "No module set the default hash function.", ExitCode.BLAZE_INTERNAL_ERROR, e);
     }
-
     Path.setFileSystemForSerialization(fs);
     SubprocessBuilder.setSubprocessFactory(subprocessFactoryImplementation());
 
diff --git a/src/main/java/com/google/devtools/build/lib/unix/UnixFileSystem.java b/src/main/java/com/google/devtools/build/lib/unix/UnixFileSystem.java
index 5d507c3..949be83 100644
--- a/src/main/java/com/google/devtools/build/lib/unix/UnixFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/unix/UnixFileSystem.java
@@ -23,6 +23,7 @@
 import com.google.devtools.build.lib.unix.NativePosixFiles.ReadTypes;
 import com.google.devtools.build.lib.vfs.AbstractFileSystemWithCustomStat;
 import com.google.devtools.build.lib.vfs.DigestHashFunction;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import com.google.devtools.build.lib.vfs.Dirent;
 import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.Path;
@@ -38,8 +39,7 @@
 @ThreadSafe
 public class UnixFileSystem extends AbstractFileSystemWithCustomStat {
 
-  public UnixFileSystem() {
-  }
+  public UnixFileSystem() throws DefaultHashFunctionNotSetException {}
 
   public UnixFileSystem(DigestHashFunction hashFunction) {
     super(hashFunction);
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystem.java
index 096ca50..771e073 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystem.java
@@ -16,6 +16,7 @@
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
@@ -30,7 +31,7 @@
   protected static final String ERR_PERMISSION_DENIED = " (Permission denied)";
   protected static final Profiler profiler = Profiler.instance();
 
-  public AbstractFileSystem() {}
+  public AbstractFileSystem() throws DefaultHashFunctionNotSetException {}
 
   public AbstractFileSystem(DigestHashFunction digestFunction) {
     super(digestFunction);
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystemWithCustomStat.java b/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystemWithCustomStat.java
index 2a2b06b..3058de3 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystemWithCustomStat.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/AbstractFileSystemWithCustomStat.java
@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.vfs;
 
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import java.io.IOException;
 
 /**
@@ -22,7 +23,7 @@
  */
 public abstract class AbstractFileSystemWithCustomStat extends AbstractFileSystem {
 
-  public AbstractFileSystemWithCustomStat() {}
+  public AbstractFileSystemWithCustomStat() throws DefaultHashFunctionNotSetException {}
 
   public AbstractFileSystemWithCustomStat(DigestHashFunction hashFunction) {
     super(hashFunction);
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/DigestHashFunction.java b/src/main/java/com/google/devtools/build/lib/vfs/DigestHashFunction.java
index 3f4b94f..b100940 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/DigestHashFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/DigestHashFunction.java
@@ -133,19 +133,20 @@
    * {@link #setDefault(DigestHashFunction)}. Once this value is set, it's a constant, so to prevent
    * blocking calls, users should cache this value if needed.
    *
-   * @throws DefaultNotSetException if the default has not yet been set by a previous call to {@link
-   *     #setDefault}.
+   * @throws DefaultHashFunctionNotSetException if the default has not yet been set by a previous
+   *     call to {@link #setDefault}.
    */
-  public static synchronized DigestHashFunction getDefault() throws DefaultNotSetException {
+  public static synchronized DigestHashFunction getDefault()
+      throws DefaultHashFunctionNotSetException {
     if (!defaultHasBeenSet) {
-      throw new DefaultNotSetException("DigestHashFunction default has not been set");
+      throw new DefaultHashFunctionNotSetException("DigestHashFunction default has not been set");
     }
     return defaultHash;
   }
 
   /** Indicates that the default has not been initialized. */
-  public static final class DefaultNotSetException extends Exception {
-    DefaultNotSetException(String message) {
+  public static final class DefaultHashFunctionNotSetException extends Exception {
+    DefaultHashFunctionNotSetException(String message) {
       super(message);
     }
   }
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java
index 048cd93..dc0020c 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/FileSystem.java
@@ -21,7 +21,7 @@
 import com.google.common.io.ByteSource;
 import com.google.common.io.CharStreams;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
-import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultNotSetException;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
@@ -39,19 +39,8 @@
 
   private final DigestHashFunction digestFunction;
 
-  public FileSystem() {
-    DigestHashFunction defaultHash;
-    try {
-      defaultHash = DigestHashFunction.getDefault();
-    } catch (DefaultNotSetException e) {
-      // For now, be tolerant for cases where the default has not been set, and fallback to MD5, the
-      // old default.
-      // TODO(b/109764197): Remove this, third_party uses of this library should set their own
-      // default, and tests should either set their own default or be able to be run with multiple
-      // digest functions.
-      defaultHash = DigestHashFunction.MD5;
-    }
-    digestFunction = defaultHash;
+  public FileSystem() throws DefaultHashFunctionNotSetException {
+    digestFunction = DigestHashFunction.getDefault();
   }
 
   public FileSystem(DigestHashFunction digestFunction) {
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/JavaIoFileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/JavaIoFileSystem.java
index 38c8d4c..de2698a 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/JavaIoFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/JavaIoFileSystem.java
@@ -19,6 +19,7 @@
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
@@ -52,7 +53,7 @@
   protected static final String ERR_NO_SUCH_FILE_OR_DIR = " (No such file or directory)";
   protected static final String ERR_NOT_A_DIRECTORY = " (Not a directory)";
 
-  public JavaIoFileSystem() {
+  public JavaIoFileSystem() throws DefaultHashFunctionNotSetException {
     this.clock = new JavaClock();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystem.java
index 0aa71c8..7c85855 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystem.java
@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.vfs;
 
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import java.io.IOException;
 import java.io.OutputStream;
 
@@ -36,8 +37,7 @@
  */
 public abstract class ReadonlyFileSystem extends AbstractFileSystem {
 
-  protected ReadonlyFileSystem() {
-  }
+  protected ReadonlyFileSystem() throws DefaultHashFunctionNotSetException {}
 
   public ReadonlyFileSystem(DigestHashFunction digestFunction) {
     super(digestFunction);
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystemWithCustomStat.java b/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystemWithCustomStat.java
index ff320b5..0eb5895 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystemWithCustomStat.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/ReadonlyFileSystemWithCustomStat.java
@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.vfs;
 
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import java.io.IOException;
 import java.io.OutputStream;
 
@@ -21,8 +22,7 @@
  */
 public abstract class ReadonlyFileSystemWithCustomStat extends AbstractFileSystemWithCustomStat {
 
-  protected ReadonlyFileSystemWithCustomStat() {
-  }
+  protected ReadonlyFileSystemWithCustomStat() throws DefaultHashFunctionNotSetException {}
 
   public ReadonlyFileSystemWithCustomStat(DigestHashFunction hashFunction) {
     super(hashFunction);
diff --git a/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java b/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java
index 869ba85..d39173a 100644
--- a/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java
@@ -18,6 +18,7 @@
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
 import com.google.devtools.build.lib.vfs.DigestHashFunction;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.JavaIoFileSystem;
 import com.google.devtools.build.lib.vfs.Path;
@@ -37,7 +38,7 @@
   public static final LinkOption[] NO_OPTIONS = new LinkOption[0];
   public static final LinkOption[] NO_FOLLOW = new LinkOption[] {LinkOption.NOFOLLOW_LINKS};
 
-  public WindowsFileSystem() {}
+  public WindowsFileSystem() throws DefaultHashFunctionNotSetException {}
 
   public WindowsFileSystem(DigestHashFunction hashFunction) {
     super(hashFunction);
diff --git a/src/test/java/com/google/devtools/build/lib/vfs/DigestHashFunctionGlobalsTest.java b/src/test/java/com/google/devtools/build/lib/vfs/DigestHashFunctionGlobalsTest.java
index 77f7b62..a822da0 100644
--- a/src/test/java/com/google/devtools/build/lib/vfs/DigestHashFunctionGlobalsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/vfs/DigestHashFunctionGlobalsTest.java
@@ -17,6 +17,7 @@
 import static com.google.devtools.build.lib.testutil.MoreAsserts.assertThrows;
 
 import com.google.common.hash.Hashing;
+import com.google.devtools.build.lib.vfs.DigestHashFunction.DefaultHashFunctionNotSetException;
 import com.google.devtools.build.lib.vfs.DigestHashFunction.DigestFunctionConverter;
 import java.lang.reflect.Field;
 import org.junit.Before;
@@ -88,8 +89,7 @@
 
   @Test
   public void unsetDefaultThrows() {
-    assertThrows(
-        DigestHashFunction.DefaultNotSetException.class, () -> DigestHashFunction.getDefault());
+    assertThrows(DefaultHashFunctionNotSetException.class, () -> DigestHashFunction.getDefault());
   }
 
   @Test