diff --git a/src/conf.h b/src/conf.h
index 9d8befda..9db19dda 100644
--- a/src/conf.h
+++ b/src/conf.h
@@ -236,6 +236,11 @@ typedef unsigned char   upx_byte;
 #undef PAGE_MASK
 #undef PAGE_SIZE
 
+#if !defined(O_BINARY) || (O_BINARY+0 == 0)
+#  if (ACC_OS_CYGWIN || ACC_OS_DOS16 || ACC_OS_DOS32 || ACC_OS_EMX || ACC_OS_OS2 || ACC_OS_OS216 || ACC_OS_WIN16 || ACC_OS_WIN32 || ACC_OS_WIN64)
+#    error "missing O_BINARY"
+#  endif
+#endif
 #if !defined(O_BINARY)
 #  define O_BINARY  0
 #endif
diff --git a/src/file.cpp b/src/file.cpp
index 0f93956e..548ee238 100644
--- a/src/file.cpp
+++ b/src/file.cpp
@@ -429,7 +429,7 @@ off_t OutputFile::seek(upx_int64_t off64, int whence)
 //{
 //    fsync(_fd);
 //    InputFile infile;
-//    infile.open(this->getName(), O_RDONLY);
+//    infile.open(this->getName(), O_RDONLY | O_BINARY);
 //    infile.seek(this->tell(), SEEK_SET);
 //    return infile.read(buf, len);
 //}
@@ -459,8 +459,8 @@ off_t OutputFile::unset_extent()
 void OutputFile::dump(const char *name, const void *buf, int len, int flags)
 {
     if (flags < 0)
-         flags = O_CREAT | O_BINARY | O_TRUNC;
-    flags |= O_WRONLY;
+         flags = O_CREAT | O_TRUNC;
+    flags |= O_WRONLY | O_BINARY;
     OutputFile f;
     f.open(name, flags, 0600);
     f.write(buf, len);
diff --git a/src/p_djgpp2.cpp b/src/p_djgpp2.cpp
index 0b50edb9..b9c77590 100644
--- a/src/p_djgpp2.cpp
+++ b/src/p_djgpp2.cpp
@@ -170,9 +170,9 @@ static void handle_allegropak(InputFile *fi, OutputFile *fo)
         if (memcmp(buf, "slh+", 4) != 0)
             return;
         pfsize = get_be32_signed(buf+4);
-        if (pfsize <= 8 || (off_t) pfsize >= (off_t) fi->st.st_size)
+        if (pfsize <= 8 || pfsize >= (off_t) fi->st.st_size)
             return;
-        fi->seek(-pfsize, SEEK_END);
+        fi->seek(-(off_t)pfsize, SEEK_END);
     } catch (const IOException&) {
         return;
     }
diff --git a/src/p_unix.cpp b/src/p_unix.cpp
index 5e99d4dc..dca7000e 100644
--- a/src/p_unix.cpp
+++ b/src/p_unix.cpp
@@ -512,7 +512,7 @@ int PackUnix::canUnpack()
         bufsize = fi->st_size();
     MemBuffer buf(bufsize);
 
-    fi->seek(-bufsize, SEEK_END);
+    fi->seek(-(off_t)bufsize, SEEK_END);
     fi->readx(buf, bufsize);
     int i = bufsize;
     while (i > small && 0 == buf[--i]) { }
diff --git a/src/packer.cpp b/src/packer.cpp
index 50ffb76e..e002565b 100644
--- a/src/packer.cpp
+++ b/src/packer.cpp
@@ -626,9 +626,9 @@ unsigned Packer::getRandomId() const
     unsigned id = 0;
 #if 0 && defined(__unix__)
     // Don't consume precious bytes from /dev/urandom.
-    int fd = open("/dev/urandom", O_RDONLY);
+    int fd = open("/dev/urandom", O_RDONLY | O_BINARY);
     if (fd < 0)
-        fd = open("/dev/random", O_RDONLY);
+        fd = open("/dev/random", O_RDONLY | O_BINARY);
     if (fd >= 0)
     {
         if (read(fd, &id, 4) != 4)
diff --git a/src/util.cpp b/src/util.cpp
index b0cf3984..9b7888ed 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -392,7 +392,7 @@ bool file_exists(const char *name)
     struct stat st;
 
     /* return true if we can open it */
-    fd = open(name, O_RDONLY, 0);
+    fd = open(name, O_RDONLY | O_BINARY, 0);
     if (fd >= 0)
     {
         (void) close(fd);