diff --git a/c/builtins.c b/c/builtins.c
index dd7e35c..0891ae2 100644
--- a/c/builtins.c
+++ b/c/builtins.c
@@ -27,7 +27,7 @@
 #include "htable.h"
 #include "htableh_inc.h"
 #include "bitvector.h"
-#include "dirpath.h"
+#include "fs.h"
 #include "random.h"
 #include "llt.h"
 
diff --git a/c/dirpath.h b/c/dirpath.h
deleted file mode 100644
index b4e8444..0000000
--- a/c/dirpath.h
+++ /dev/null
@@ -1,19 +0,0 @@
-#ifdef WIN32
-#define PATHSEP '\\'
-#define PATHSEPSTRING "\\"
-#define PATHLISTSEP ';'
-#define PATHLISTSEPSTRING ";"
-#define ISPATHSEP(c) ((c) == '/' || (c) == '\\')
-#define MAXPATHLEN 1024
-#else
-#define PATHSEP '/'
-#define PATHSEPSTRING "/"
-#define PATHLISTSEP ':'
-#define PATHLISTSEPSTRING ":"
-#define ISPATHSEP(c) ((c) == '/')
-#endif
-
-void get_cwd(char *buf, size_t size);
-int set_cwd(char *buf);
-char *get_exename(char *buf, size_t size);
-void path_to_dirname(char *path);
diff --git a/c/equalhash.c b/c/equalhash.c
index 6811138..3c9f813 100644
--- a/c/equalhash.c
+++ b/c/equalhash.c
@@ -16,7 +16,7 @@
 #include "htable.h"
 #include "htableh_inc.h"
 #include "bitvector.h"
-#include "dirpath.h"
+#include "fs.h"
 #include "random.h"
 #include "llt.h"
 
diff --git a/c/flisp.c b/c/flisp.c
index eb29a27..3cb3cfd 100644
--- a/c/flisp.c
+++ b/c/flisp.c
@@ -55,7 +55,7 @@
 #include "htable.h"
 #include "htableh_inc.h"
 #include "bitvector.h"
-#include "dirpath.h"
+#include "fs.h"
 #include "random.h"
 #include "llt.h"
 
diff --git a/c/flmain.c b/c/flmain.c
index 506fed8..7a6e05c 100644
--- a/c/flmain.c
+++ b/c/flmain.c
@@ -15,7 +15,7 @@
 #include "htable.h"
 #include "htableh_inc.h"
 #include "bitvector.h"
-#include "dirpath.h"
+#include "fs.h"
 #include "random.h"
 #include "llt.h"
 
@@ -50,8 +50,7 @@ int main(int argc, char *argv[])
     if (exedir == NULL) {
         snprintf(fname_buf, sizeof(fname_buf), "%s", bootfile);
     } else {
-        snprintf(fname_buf, sizeof(fname_buf), "%s%s%s", exedir,
-                 PATHSEPSTRING, bootfile);
+        snprintf(fname_buf, sizeof(fname_buf), "%s/%s", exedir, bootfile);
     }
 
     value_t args[2];
diff --git a/c/fs.h b/c/fs.h
new file mode 100644
index 0000000..a73076a
--- /dev/null
+++ b/c/fs.h
@@ -0,0 +1,4 @@
+void path_to_dirname(char *path);
+void get_cwd(char *buf, size_t size);
+int set_cwd(char *buf);
+char *get_exename(char *buf, size_t size);
diff --git a/c/fs_darwin.c b/c/fs_darwin.c
new file mode 100644
index 0000000..da8f2db
--- /dev/null
+++ b/c/fs_darwin.c
@@ -0,0 +1,11 @@
+#include <mach-o/dyld.h>
+
+#include "fs.h"
+
+char *get_exename(char *buf, size_t size)
+{
+    uint32_t bufsize = (uint32_t)size;
+    if (_NSGetExecutablePath(buf, &bufsize))
+        return NULL;
+    return buf;
+}
diff --git a/c/fs_freebsd.c b/c/fs_freebsd.c
new file mode 100644
index 0000000..47a78dc
--- /dev/null
+++ b/c/fs_freebsd.c
@@ -0,0 +1,17 @@
+#include <sys/types.h>
+
+#include <sys/sysctl.h>
+
+#include "fs.h"
+
+char *get_exename(char *buf, size_t size)
+{
+    int mib[4];
+    mib[0] = CTL_KERN;
+    mib[1] = KERN_PROC;
+    mib[2] = KERN_PROC_PATHNAME;
+    mib[3] = -1;
+    sysctl(mib, 4, buf, &size, NULL, 0);
+
+    return buf;
+}
diff --git a/c/fs_linux.c b/c/fs_linux.c
new file mode 100644
index 0000000..faaa40a
--- /dev/null
+++ b/c/fs_linux.c
@@ -0,0 +1,33 @@
+#include <string.h>
+#include <unistd.h>
+
+#include "fs.h"
+
+char *get_exename(char *buf, size_t size)
+{
+    char linkname[64]; /* /proc/<pid>/exe */
+    pid_t pid;
+    ssize_t ret;
+
+    /* Get our PID and build the name of the link in /proc */
+    pid = getpid();
+
+    if (snprintf(linkname, sizeof(linkname), "/proc/%i/exe", pid) < 0)
+        return NULL;
+
+    /* Now read the symbolic link */
+    ret = readlink(linkname, buf, size);
+
+    /* In case of an error, leave the handling up to the caller */
+    if (ret == -1)
+        return NULL;
+
+    /* Report insufficient buffer size */
+    if ((size_t)ret >= size)
+        return NULL;
+
+    /* Ensure proper NUL termination */
+    buf[ret] = 0;
+
+    return buf;
+}
diff --git a/c/dirpath.c b/c/fs_openbsd.c
similarity index 62%
rename from c/dirpath.c
rename to c/fs_openbsd.c
index 2550418..48e0d05 100644
--- a/c/dirpath.c
+++ b/c/fs_openbsd.c
@@ -1,98 +1,13 @@
-#include <stdint.h>
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-#include <time.h>
-#include <assert.h>
-#include <errno.h>
-#include <limits.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-
-#include "dtypes.h"
-
-#ifdef WIN32
-#include <malloc.h>
-#include <sys/timeb.h>
-#include <windows.h>
-#undef NO_ERROR
-#undef MOD_SHIFT
-#undef TRUE
-#undef FALSE
-#undef VOID
-#else
-#include <sys/time.h>
-#include <sys/poll.h>
-#include <unistd.h>
-#endif
-
-#include "dirpath.h"
-
-void get_cwd(char *buf, size_t size)
-{
-#ifndef WIN32
-    getcwd(buf, size);
-#else
-    GetCurrentDirectory(size, buf);
-#endif
-}
-
-int set_cwd(char *buf)
-{
-#ifndef WIN32
-    if (chdir(buf) == -1)
-        return 1;
-#else
-    if (SetCurrentDirectory(buf) == 0)
-        return 1;
-#endif
-    return 0;
-}
-
-// destructively convert path to directory part
-void path_to_dirname(char *path)
-{
-    char *sep = strrchr(path, PATHSEP);
-    if (sep != NULL) {
-        *sep = '\0';
-    } else {
-        path[0] = '\0';
-    }
-}
-
-#ifdef LINUX
-char *get_exename(char *buf, size_t size)
-{
-    char linkname[64]; /* /proc/<pid>/exe */
-    pid_t pid;
-    ssize_t ret;
-
-    /* Get our PID and build the name of the link in /proc */
-    pid = getpid();
-
-    if (snprintf(linkname, sizeof(linkname), "/proc/%i/exe", pid) < 0)
-        return NULL;
-
-    /* Now read the symbolic link */
-    ret = readlink(linkname, buf, size);
-
-    /* In case of an error, leave the handling up to the caller */
-    if (ret == -1)
-        return NULL;
-
-    /* Report insufficient buffer size */
-    if ((size_t)ret >= size)
-        return NULL;
-
-    /* Ensure proper NUL termination */
-    buf[ret] = 0;
-
-    return buf;
-}
-#elif defined(OPENBSD)
 #include <sys/param.h>
+
+#include <sys/stat.h>
 #include <sys/sysctl.h>
 
+#include <stdlib.h>
+#include <string.h>
+
+#include "fs.h"
+
 char *get_exename(char *buf, size_t size)
 {
     int mib[4];
@@ -197,36 +112,3 @@ char *get_exename(char *buf, size_t size)
 
     return buf;
 }
-#elif defined(FREEBSD)
-#include <sys/types.h>
-#include <sys/sysctl.h>
-
-char *get_exename(char *buf, size_t size)
-{
-    int mib[4];
-    mib[0] = CTL_KERN;
-    mib[1] = KERN_PROC;
-    mib[2] = KERN_PROC_PATHNAME;
-    mib[3] = -1;
-    sysctl(mib, 4, buf, &size, NULL, 0);
-
-    return buf;
-}
-#elif defined(WIN32)
-char *get_exename(char *buf, size_t size)
-{
-    if (GetModuleFileName(NULL, buf, size) == 0)
-        return NULL;
-
-    return buf;
-}
-#elif defined(MACOSX)
-#include <mach-o/dyld.h>
-char *get_exename(char *buf, size_t size)
-{
-    uint32_t bufsize = (uint32_t)size;
-    if (_NSGetExecutablePath(buf, &bufsize))
-        return NULL;
-    return buf;
-}
-#endif
diff --git a/c/fs_unix.c b/c/fs_unix.c
new file mode 100644
index 0000000..4415a39
--- /dev/null
+++ b/c/fs_unix.c
@@ -0,0 +1,23 @@
+#include <string.h>
+#include <unistd.h>
+
+#include "fs.h"
+
+void path_to_dirname(char *path)
+{
+    char *p;
+
+    if (!(p = strrchr(path, '/'))) {
+        p = path;
+    }
+    *p = '\0';
+}
+
+void get_cwd(char *buf, size_t size) { getcwd(buf, size); }
+
+int set_cwd(char *buf)
+{
+    if (chdir(buf) == -1)
+        return 1;
+    return 0;
+}
diff --git a/c/fs_windows.c b/c/fs_windows.c
new file mode 100644
index 0000000..cc51c96
--- /dev/null
+++ b/c/fs_windows.c
@@ -0,0 +1,33 @@
+#include <windows.h>
+
+#include "fs.h"
+
+void path_to_dirname(char *path)
+{
+    char *p;
+
+    p = strchr(path, 0);
+    while (p > path) {
+        p--;
+        if ((*p == '/') || (*p == '\\')) {
+            break;
+        }
+    }
+    *p = '\0';
+}
+
+void get_cwd(char *buf, size_t size) { GetCurrentDirectory(size, buf); }
+
+int set_cwd(char *buf)
+{
+    if (SetCurrentDirectory(buf) == 0)
+        return 1;
+    return 0;
+}
+
+char *get_exename(char *buf, size_t size)
+{
+    if (GetModuleFileName(NULL, buf, size) == 0)
+        return NULL;
+    return buf;
+}
diff --git a/c/iostream.c b/c/iostream.c
index 89eb8d4..6c0506f 100644
--- a/c/iostream.c
+++ b/c/iostream.c
@@ -17,7 +17,7 @@
 #include "htable.h"
 #include "htableh_inc.h"
 #include "bitvector.h"
-#include "dirpath.h"
+#include "fs.h"
 #include "random.h"
 #include "llt.h"
 
diff --git a/c/string.c b/c/string.c
index 62a8a2f..736ef17 100644
--- a/c/string.c
+++ b/c/string.c
@@ -26,7 +26,7 @@
 #include "htable.h"
 #include "htableh_inc.h"
 #include "bitvector.h"
-#include "dirpath.h"
+#include "fs.h"
 #include "random.h"
 #include "llt.h"
 
diff --git a/c/table.c b/c/table.c
index f8220fe..ea62200 100644
--- a/c/table.c
+++ b/c/table.c
@@ -17,7 +17,7 @@
 #include "htable.h"
 #include "htableh_inc.h"
 #include "bitvector.h"
-#include "dirpath.h"
+#include "fs.h"
 #include "random.h"
 #include "llt.h"
 
diff --git a/scripts/build.sh b/scripts/build.sh
index f0178a1..e874771 100755
--- a/scripts/build.sh
+++ b/scripts/build.sh
@@ -2,10 +2,11 @@
 set -eu
 CC="${CC:-clang}"
 CFLAGS="-Wall -Wextra -Wno-strict-aliasing -std=gnu99"
-CFLAGS="$CFLAGS -O2"  # -falign-functions
+CFLAGS="$CFLAGS -O2" # -falign-functions
 CFLAGS="$CFLAGS -I ../c -D NDEBUG -D USE_COMPUTED_GOTO"
 LFLAGS="-lm"
-builddir="build-$(uname | tr A-Z- a-z_)-$(uname -m | tr A-Z- a-z_)"
+os="$(uname | tr A-Z- a-z_)"
+builddir="build-$os-$(uname -m | tr A-Z- a-z_)"
 cd "$(dirname "$0")"/..
 echo "Entering directory '$PWD'"
 set -x
@@ -15,14 +16,16 @@ find "$builddir" -mindepth 1 -delete
 cd "$builddir"
 echo "Entering directory '$PWD'"
 set -x
+ln -s ../scheme-boot/flisp.boot flisp.boot
 $CC $CFLAGS -c ../c/bitvector-ops.c
 $CC $CFLAGS -c ../c/bitvector.c
 $CC $CFLAGS -c ../c/builtins.c
-$CC $CFLAGS -c ../c/dirpath.c
 $CC $CFLAGS -c ../c/dump.c
 $CC $CFLAGS -c ../c/equalhash.c
 $CC $CFLAGS -c ../c/flisp.c
 $CC $CFLAGS -c ../c/flmain.c
+$CC $CFLAGS -c ../c/fs_"$os".c
+$CC $CFLAGS -c ../c/fs_unix.c
 $CC $CFLAGS -c ../c/hashing.c
 $CC $CFLAGS -c ../c/htable.c
 $CC $CFLAGS -c ../c/int2str.c
@@ -37,11 +40,11 @@ $CC $CFLAGS -c ../c/table.c
 $CC $CFLAGS -c ../c/timefuncs.c
 $CC $CFLAGS -c ../c/utf8.c
 $CC $LFLAGS -o flisp -lm \
-    bitvector-ops.o bitvector.o builtins.o dirpath.o dump.o \
-    equalhash.o flisp.o flmain.o hashing.o htable.o int2str.o \
-    ios.o iostream.o lltinit.o ptrhash.o random.o socket.o \
-    string.o table.o timefuncs.o utf8.o
-ln -s ../scheme-boot/flisp.boot flisp.boot
+        bitvector-ops.o bitvector.o builtins.o dump.o \
+        equalhash.o flisp.o flmain.o fs_"$os".o fs_unix.o \
+        hashing.o htable.o int2str.o \
+        ios.o iostream.o lltinit.o ptrhash.o random.o socket.o \
+        string.o table.o timefuncs.o utf8.o
 { set +x; } 2>/dev/null
 cd ../scheme-core
 echo "Entering directory '$PWD'"