diff --git a/expected/wasm32-wasi/defined-symbols.txt b/expected/wasm32-wasi/defined-symbols.txt
index 6c0dc4e24..716b119a8 100644
--- a/expected/wasm32-wasi/defined-symbols.txt
+++ b/expected/wasm32-wasi/defined-symbols.txt
@@ -242,6 +242,7 @@ __unlist_locked_file
 __uselocale
 __utc
 __wasilibc_fd_renumber
+__wasilibc_find_relpath
 __wasilibc_init_preopen
 __wasilibc_register_preopened_fd
 __wasilibc_rmdirat
diff --git a/expected/wasm32-wasi/include-all.c b/expected/wasm32-wasi/include-all.c
index 8295222d1..62760dd2d 100644
--- a/expected/wasm32-wasi/include-all.c
+++ b/expected/wasm32-wasi/include-all.c
@@ -183,6 +183,7 @@
 #include <utime.h>
 #include <values.h>
 #include <wasi/core.h>
+#include <wasi/libc-find-relpath.h>
 #include <wasi/libc.h>
 #include <wchar.h>
 #include <wctype.h>
diff --git a/expected/wasm32-wasi/predefined-macros.txt b/expected/wasm32-wasi/predefined-macros.txt
index 7c89429ec..9b636b8d1 100644
--- a/expected/wasm32-wasi/predefined-macros.txt
+++ b/expected/wasm32-wasi/predefined-macros.txt
@@ -3622,6 +3622,7 @@
 #define __va_copy(d,s) __builtin_va_copy(d,s)
 #define __wasi__ 1
 #define __wasi_core_h 
+#define __wasi_libc_find_relpath_h 
 #define __wasi_libc_h 
 #define __wasilibc___errno_values_h 
 #define __wasilibc___fd_set_h 
diff --git a/libc-bottom-half/headers/public/wasi/libc-find-relpath.h b/libc-bottom-half/headers/public/wasi/libc-find-relpath.h
new file mode 100644
index 000000000..9f5fab3d8
--- /dev/null
+++ b/libc-bottom-half/headers/public/wasi/libc-find-relpath.h
@@ -0,0 +1,25 @@
+#ifndef __wasi_libc_find_relpath_h
+#define __wasi_libc_find_relpath_h
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Look up the given path in the preopened directory map. If a suitable
+ * entry is found, return its directory file descriptor, and store the
+ * computed relative path in *relative_path. Ignore preopened directories
+ * which don't provide the specified rights.
+ *
+ * Returns -1 if no directories were suitable.
+ */
+int __wasilibc_find_relpath(const char *path,
+                            __wasi_rights_t rights_base,
+                            __wasi_rights_t rights_inheriting,
+                            const char **relative_path);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/libc-bottom-half/libpreopen/include/libpreopen.h b/libc-bottom-half/libpreopen/include/libpreopen.h
index 8185dcfa0..9c86b9fe1 100644
--- a/libc-bottom-half/libpreopen/include/libpreopen.h
+++ b/libc-bottom-half/libpreopen/include/libpreopen.h
@@ -82,6 +82,12 @@ struct po_relpath {
 	/** The path, relative to the directory represented by @ref dirfd */
 	const char *relative_path;
 };
+#ifdef __wasilibc_unmodified_upstream
+#else
+// This functionality is exposed in a libc header, so include that header
+// and use its declarations.
+#include <wasi/libc-find-relpath.h>
+#endif
 
 /**
  * Create a @ref po_map of at least the specified capacity.
diff --git a/libc-bottom-half/libpreopen/lib/po_libc_wrappers.c b/libc-bottom-half/libpreopen/lib/po_libc_wrappers.c
index a6d444531..5aead7931 100644
--- a/libc-bottom-half/libpreopen/lib/po_libc_wrappers.c
+++ b/libc-bottom-half/libpreopen/lib/po_libc_wrappers.c
@@ -682,4 +682,14 @@ __wasilibc_register_preopened_fd(int fd, const char *path)
 
 	return 0;
 }
+
+int __wasilibc_find_relpath(const char *path,
+                            __wasi_rights_t rights_base,
+                            __wasi_rights_t rights_inheriting,
+                            const char **relpath)
+{
+    struct po_relpath rel = find_relative(path, rights_base, rights_inheriting);
+    *relpath = rel.relative_path;
+    return rel.dirfd;
+}
 #endif