diff --git a/libc/stdio/local.h b/libc/stdio/local.h
index 6fb2c0d..bf6a8f8 100644
--- a/libc/stdio/local.h
+++ b/libc/stdio/local.h
@@ -127,10 +127,11 @@
 // Values for `__sFILE::_flags`.
 #define __SLBF 0x0001  // Line buffered.
 #define __SNBF 0x0002  // Unbuffered.
-// RD and WR are never simultaneously asserted: use _SRW instead.
-#define __SRD  0x0004  // OK to read.
-#define __SWR  0x0008  // OK to write.
-#define __SRW  0x0010  // Open for reading & writing.
+// __SRD and __SWR are mutually exclusive because they indicate what we did last.
+// If you want to know whether we were opened read-write, check __SRW instead.
+#define __SRD  0x0004  // Last operation was read.
+#define __SWR  0x0008  // Last operation was write.
+#define __SRW  0x0010  // Was opened for reading & writing.
 #define __SEOF 0x0020  // Found EOF.
 #define __SERR 0x0040  // Found error.
 #define __SMBF 0x0080  // `_buf` is from malloc.
diff --git a/libc/stdio/stdio_ext.cpp b/libc/stdio/stdio_ext.cpp
index ebc705c..8cf4f4b 100644
--- a/libc/stdio/stdio_ext.cpp
+++ b/libc/stdio/stdio_ext.cpp
@@ -39,17 +39,13 @@
   return fp->_bf._size;
 }
 
-/* For a _SRW stream, we don't know whether we last read or wrote.
 int __freading(FILE* fp) {
-  return (fp->_flags & _SRD) != 0 || ...;
+  return (fp->_flags & __SRD) != 0;
 }
-*/
 
-/* For a _SRW stream, we don't know whether we last read or wrote.
-int __fwriting(FILE*) {
-  return (fp->_flags & _SWR) != 0 || ...;
+int __fwriting(FILE* fp) {
+  return (fp->_flags & __SWR) != 0;
 }
-*/
 
 int __freadable(FILE* fp) {
   return (fp->_flags & (__SRD|__SRW)) != 0;