diff --git a/libc/src/__support/File/file.cpp b/libc/src/__support/File/file.cpp
--- a/libc/src/__support/File/file.cpp
+++ b/libc/src/__support/File/file.cpp
@@ -57,7 +57,7 @@
   // If the remaining bytes from |data| can fit in the buffer, write
   // into it. Else, write it directly to the platform stream.
   size_t remaining = len - write_size;
-  if (remaining <= len) {
+  if (remaining <= bufsize) {
     // TODO: Replace the for loop below with a call to internal memcpy.
     for (size_t i = 0; i < remaining; ++i)
       bufref[i] = dataref[i];
diff --git a/libc/test/src/__support/File/file_test.cpp b/libc/test/src/__support/File/file_test.cpp
--- a/libc/test/src/__support/File/file_test.cpp
+++ b/libc/test/src/__support/File/file_test.cpp
@@ -335,3 +335,33 @@
 
   ASSERT_EQ(f->close(), 0);
 }
+
+TEST(LlvmLibcFileTest, SmallBuffer) {
+  const char WRITE_DATA[] = "small buffer";
+  constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+  constexpr size_t FILE_BUFFER_SIZE = sizeof(WRITE_DATA) / 2 - 1;
+  char file_buffer[FILE_BUFFER_SIZE];
+  StringFile *f = new_string_file(file_buffer, FILE_BUFFER_SIZE, 0, false, "w");
+
+  ASSERT_EQ(WRITE_SIZE, f->write(WRITE_DATA, WRITE_SIZE));
+  // Since data much larger than the buffer is being written, all of it should
+  // be available in the file without a flush operation.
+  EXPECT_EQ(f->get_pos(), sizeof(WRITE_DATA));
+  ASSERT_STREQ(f->get_str(), WRITE_DATA);
+
+  ASSERT_EQ(f->close(), 0);
+}
+
+TEST(LlvmLibcFileTest, ZeroLengthBuffer) {
+  const char WRITE_DATA[] = "small buffer";
+  constexpr size_t WRITE_SIZE = sizeof(WRITE_DATA);
+  StringFile *f = new_string_file(nullptr, 0, 0, true, "w");
+
+  ASSERT_EQ(WRITE_SIZE, f->write(WRITE_DATA, WRITE_SIZE));
+  // Since there is no buffer space, all of the written data should
+  // be available in the file without a flush operation.
+  EXPECT_EQ(f->get_pos(), sizeof(WRITE_DATA));
+  ASSERT_STREQ(f->get_str(), WRITE_DATA);
+
+  ASSERT_EQ(f->close(), 0);
+}