diff --git a/libc/stdio/local.h b/libc/stdio/local.h
index 7188c74..a4c0264 100644
--- a/libc/stdio/local.h
+++ b/libc/stdio/local.h
@@ -92,6 +92,15 @@
 
 	/* Unix stdio files get aligned to block boundaries on fseek() */
 	int	_blksize;	/* stat.st_blksize (may be != _bf._size) */
+
+	fpos_t _unused_0; // This was the `_offset` field (see below).
+
+	// Do not add new fields here. (Or remove or change the size of any above.)
+	// Although bionic currently exports `stdin`, `stdout`, and `stderr` symbols,
+	// that still hasn't made it to the NDK. All NDK-built apps index directly
+	// into an array of this struct (which was in <stdio.h> historically), so if
+	// you need to make any changes, they need to be in the `__sfileext` struct
+	// below, and accessed via `_EXT`.
 };
 
 /*
diff --git a/libc/stdio/stdio.cpp b/libc/stdio/stdio.cpp
index 1066d7f..7e9c439 100644
--- a/libc/stdio/stdio.cpp
+++ b/libc/stdio/stdio.cpp
@@ -52,7 +52,7 @@
 
 #define	std(flags, file) \
 	{0,0,0,flags,file,{0,0},0,__sF+file,__sclose,__sread,__sseek,__swrite, \
-	    {(unsigned char *)(__sFext+file), 0},NULL,0,{0},{0},{0,0},0}
+	    {(unsigned char *)(__sFext+file), 0},NULL,0,{0},{0},{0,0},0,0}
 
 _THREAD_PRIVATE_MUTEX(__sfp_mutex);
 
diff --git a/tests/stdio_test.cpp b/tests/stdio_test.cpp
index 31acfec..a7df784 100644
--- a/tests/stdio_test.cpp
+++ b/tests/stdio_test.cpp
@@ -1093,3 +1093,31 @@
   fclose(fp);
 #endif
 }
+
+TEST(STDIO_TEST, lots_of_concurrent_files) {
+  std::vector<TemporaryFile*> tfs;
+  std::vector<FILE*> fps;
+
+  for (size_t i = 0; i < 256; ++i) {
+    TemporaryFile* tf = new TemporaryFile;
+    tfs.push_back(tf);
+    FILE* fp = fopen(tf->filename, "w+");
+    fps.push_back(fp);
+    fprintf(fp, "hello %zu!\n", i);
+    fflush(fp);
+  }
+
+  for (size_t i = 0; i < 256; ++i) {
+    rewind(fps[i]);
+
+    char buf[BUFSIZ];
+    ASSERT_TRUE(fgets(buf, sizeof(buf), fps[i]) != nullptr);
+
+    char expected[BUFSIZ];
+    snprintf(expected, sizeof(expected), "hello %zu!\n", i);
+    ASSERT_STREQ(expected, buf);
+
+    fclose(fps[i]);
+    delete tfs[i];
+  }
+}