diff --git a/src/java_tools/buildjar/java/com/google/devtools/build/java/turbine/javac/JavacTurbineCompiler.java b/src/java_tools/buildjar/java/com/google/devtools/build/java/turbine/javac/JavacTurbineCompiler.java
index 1a3b32f6692cb3..2db21b92db7ba1 100644
--- a/src/java_tools/buildjar/java/com/google/devtools/build/java/turbine/javac/JavacTurbineCompiler.java
+++ b/src/java_tools/buildjar/java/com/google/devtools/build/java/turbine/javac/JavacTurbineCompiler.java
@@ -16,6 +16,7 @@
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 
+import com.google.common.base.Joiner;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.jimfs.Configuration;
@@ -105,7 +106,9 @@ static JavacTurbineCompileResult compile(JavacTurbineCompileRequest request) thr
               @Override
               public FileVisitResult visitFile(Path path, BasicFileAttributes attrs)
                   throws IOException {
-                files.put(classes.relativize(path).toString(), Files.readAllBytes(path));
+                // use `/` as the directory separator for jar paths, even on Windows
+                String name = Joiner.on('/').join(classes.relativize(path));
+                files.put(name, Files.readAllBytes(path));
                 return FileVisitResult.CONTINUE;
               }
             });