diff --git a/src/common/compat.c b/src/common/compat.c
index 63bf99de68..b0a0a302c2 100644
--- a/src/common/compat.c
+++ b/src/common/compat.c
@@ -547,43 +547,3 @@ tor_getpass(const char *prompt, char *output, size_t buflen)
 #error "No implementation for tor_getpass found!"
 #endif /* defined(HAVE_READPASSPHRASE) || ... */
 }
-
-/** Return the amount of free disk space we have permission to use, in
- * bytes. Return -1 if the amount of free space can't be determined. */
-int64_t
-tor_get_avail_disk_space(const char *path)
-{
-#ifdef HAVE_STATVFS
-  struct statvfs st;
-  int r;
-  memset(&st, 0, sizeof(st));
-
-  r = statvfs(path, &st);
-  if (r < 0)
-    return -1;
-
-  int64_t result = st.f_bavail;
-  if (st.f_frsize) {
-    result *= st.f_frsize;
-  } else if (st.f_bsize) {
-    result *= st.f_bsize;
-  } else {
-    return -1;
-  }
-
-  return result;
-#elif defined(_WIN32)
-  ULARGE_INTEGER freeBytesAvail;
-  BOOL ok;
-
-  ok = GetDiskFreeSpaceEx(path, &freeBytesAvail, NULL, NULL);
-  if (!ok) {
-    return -1;
-  }
-  return (int64_t)freeBytesAvail.QuadPart;
-#else
-  (void)path;
-  errno = ENOSYS;
-  return -1;
-#endif /* defined(HAVE_STATVFS) || ... */
-}
diff --git a/src/lib/fs/freespace.c b/src/lib/fs/freespace.c
new file mode 100644
index 0000000000..926b17dbde
--- /dev/null
+++ b/src/lib/fs/freespace.c
@@ -0,0 +1,56 @@
+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#include "lib/fs/files.h"
+#include "lib/cc/torint.h"
+
+#ifdef HAVE_SYS_STATVFS_H
+#include <sys/statvfs.h>
+#endif
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+#include <string.h>
+
+/** Return the amount of free disk space we have permission to use, in
+ * bytes. Return -1 if the amount of free space can't be determined. */
+int64_t
+tor_get_avail_disk_space(const char *path)
+{
+#ifdef HAVE_STATVFS
+  struct statvfs st;
+  int r;
+  memset(&st, 0, sizeof(st));
+
+  r = statvfs(path, &st);
+  if (r < 0)
+    return -1;
+
+  int64_t result = st.f_bavail;
+  if (st.f_frsize) {
+    result *= st.f_frsize;
+  } else if (st.f_bsize) {
+    result *= st.f_bsize;
+  } else {
+    return -1;
+  }
+
+  return result;
+#elif defined(_WIN32)
+  ULARGE_INTEGER freeBytesAvail;
+  BOOL ok;
+
+  ok = GetDiskFreeSpaceEx(path, &freeBytesAvail, NULL, NULL);
+  if (!ok) {
+    return -1;
+  }
+  return (int64_t)freeBytesAvail.QuadPart;
+#else
+  (void)path;
+  errno = ENOSYS;
+  return -1;
+#endif /* defined(HAVE_STATVFS) || ... */
+}
diff --git a/src/lib/fs/include.am b/src/lib/fs/include.am
index a025eb81c0..f33e4d6430 100644
--- a/src/lib/fs/include.am
+++ b/src/lib/fs/include.am
@@ -9,6 +9,7 @@ src_lib_libtor_fs_a_SOURCES =			\
 	src/lib/fs/conffile.c			\
 	src/lib/fs/dir.c			\
 	src/lib/fs/files.c			\
+	src/lib/fs/freespace.c			\
 	src/lib/fs/lockfile.c			\
 	src/lib/fs/mmap.c			\
 	src/lib/fs/path.c			\