diff --git a/CoreFoundation/Base.subproj/ForSwiftFoundationOnly.h b/CoreFoundation/Base.subproj/ForSwiftFoundationOnly.h
index d78eeddf68..c6e63fac8e 100644
--- a/CoreFoundation/Base.subproj/ForSwiftFoundationOnly.h
+++ b/CoreFoundation/Base.subproj/ForSwiftFoundationOnly.h
@@ -64,6 +64,8 @@
 #include <sys/stat.h>
 #include <sys/syscall.h>
 #include <termios.h>
+#elif TARGET_OS_WASI
+#include <fcntl.h>
 #elif TARGET_OS_LINUX
 #include <errno.h>
 #include <features.h>
@@ -712,6 +714,15 @@ typedef struct _REPARSE_DATA_BUFFER {
 } REPARSE_DATA_BUFFER;
 #endif
 
+#if TARGET_OS_WASI
+static inline uint8_t _getConst_DT_DIR(void) { return DT_DIR; }
+static inline int32_t _getConst_O_CREAT(void) { return O_CREAT; }
+static inline int32_t _getConst_O_DIRECTORY(void) { return O_DIRECTORY; }
+static inline int32_t _getConst_O_EXCL(void) { return O_EXCL; }
+static inline int32_t _getConst_O_TRUNC(void) { return O_TRUNC; }
+static inline int32_t _getConst_O_WRONLY(void) { return O_WRONLY; }
+#endif
+
 #if !TARGET_OS_WIN32
 typedef void * _CFPosixSpawnFileActionsRef;
 typedef void * _CFPosixSpawnAttrRef;
diff --git a/Sources/Foundation/FileManager+POSIX.swift b/Sources/Foundation/FileManager+POSIX.swift
index a69d71e9f7..f2f723fa78 100644
--- a/Sources/Foundation/FileManager+POSIX.swift
+++ b/Sources/Foundation/FileManager+POSIX.swift
@@ -13,6 +13,18 @@ internal func &(left: UInt32, right: mode_t) -> mode_t {
 }
 #endif
 
+#if os(WASI)
+import WASILibc
+// wasi-libc defines the following constants in a way that Clang Importer can't
+// understand, so we need to grab them manually through ForSwiftFoundationOnly.h
+internal var DT_DIR: UInt8 { _getConst_DT_DIR() }
+internal var O_CREAT: Int32 { _getConst_O_CREAT() }
+internal var O_DIRECTORY: Int32 { _getConst_O_DIRECTORY() }
+internal var O_EXCL: Int32 { _getConst_O_EXCL() }
+internal var O_TRUNC: Int32 { _getConst_O_TRUNC() }
+internal var O_WRONLY: Int32 { _getConst_O_WRONLY() }
+#endif
+
 @_implementationOnly import CoreFoundation
 
 extension FileManager {