diff --git a/lib/uzlib/header.c b/lib/uzlib/header.c
new file mode 100644
index 0000000000..edd2b08ab5
--- /dev/null
+++ b/lib/uzlib/header.c
@@ -0,0 +1,133 @@
+/*
+ * uzlib  -  tiny deflate/inflate library (deflate, gzip, zlib)
+ *
+ * Copyright (c) 2003 by Joergen Ibsen / Jibz
+ * All Rights Reserved
+ *
+ * http://www.ibsensoftware.com/
+ *
+ * Copyright (c) 2014-2018 by Paul Sokolovsky
+ *
+ * Optimised for MicroPython:
+ * Copyright (c) 2023 by Jim Mussared
+ *
+ * This software is provided 'as-is', without any express
+ * or implied warranty.  In no event will the authors be
+ * held liable for any damages arising from the use of
+ * this software.
+ *
+ * Permission is granted to anyone to use this software
+ * for any purpose, including commercial applications,
+ * and to alter it and redistribute it freely, subject to
+ * the following restrictions:
+ *
+ * 1. The origin of this software must not be
+ *    misrepresented; you must not claim that you
+ *    wrote the original software. If you use this
+ *    software in a product, an acknowledgment in
+ *    the product documentation would be appreciated
+ *    but is not required.
+ *
+ * 2. Altered source versions must be plainly marked
+ *    as such, and must not be misrepresented as
+ *    being the original software.
+ *
+ * 3. This notice may not be removed or altered from
+ *    any source distribution.
+ */
+
+#include "uzlib.h"
+
+#define FTEXT    1
+#define FHCRC    2
+#define FEXTRA   4
+#define FNAME    8
+#define FCOMMENT 16
+
+void tinf_skip_bytes(uzlib_uncomp_t *d, int num);
+uint16_t tinf_get_uint16(uzlib_uncomp_t *d);
+
+void tinf_skip_bytes(uzlib_uncomp_t *d, int num)
+{
+    while (num--) uzlib_get_byte(d);
+}
+
+uint16_t tinf_get_uint16(uzlib_uncomp_t *d)
+{
+    unsigned int v = uzlib_get_byte(d);
+    v = (uzlib_get_byte(d) << 8) | v;
+    return v;
+}
+
+int uzlib_parse_zlib_gzip_header(uzlib_uncomp_t *d, int *wbits)
+{
+    /* -- check format -- */
+    unsigned char cmf = uzlib_get_byte(d);
+    unsigned char flg = uzlib_get_byte(d);
+
+    /* check for gzip id bytes */
+    if (cmf == 0x1f && flg == 0x8b) {
+        /* check method is deflate */
+        if (uzlib_get_byte(d) != 8) return UZLIB_DATA_ERROR;
+
+        /* get flag byte */
+        flg = uzlib_get_byte(d);
+
+        /* check that reserved bits are zero */
+        if (flg & 0xe0) return UZLIB_DATA_ERROR;
+
+        /* -- find start of compressed data -- */
+
+        /* skip rest of base header of 10 bytes */
+        tinf_skip_bytes(d, 6);
+
+        /* skip extra data if present */
+        if (flg & FEXTRA)
+        {
+           unsigned int xlen = tinf_get_uint16(d);
+           tinf_skip_bytes(d, xlen);
+        }
+
+        /* skip file name if present */
+        if (flg & FNAME) { while (uzlib_get_byte(d)); }
+
+        /* skip file comment if present */
+        if (flg & FCOMMENT) { while (uzlib_get_byte(d)); }
+
+        /* check header crc if present */
+        if (flg & FHCRC)
+        {
+           /*unsigned int hcrc =*/ tinf_get_uint16(d);
+
+            // TODO: Check!
+    //       if (hcrc != (tinf_crc32(src, start - src) & 0x0000ffff))
+    //          return UZLIB_DATA_ERROR;
+        }
+
+        /* initialize for crc32 checksum */
+        d->checksum_type = UZLIB_CHKSUM_CRC;
+        d->checksum = ~0;
+
+        return UZLIB_HEADER_GZIP;
+    } else {
+       /* check checksum */
+       if ((256*cmf + flg) % 31) return UZLIB_DATA_ERROR;
+
+       /* check method is deflate */
+       if ((cmf & 0x0f) != 8) return UZLIB_DATA_ERROR;
+
+       /* check window size is valid */
+       if ((cmf >> 4) > 7) return UZLIB_DATA_ERROR;
+
+       /* check there is no preset dictionary */
+       if (flg & 0x20) return UZLIB_DATA_ERROR;
+
+       /* initialize for adler32 checksum */
+       d->checksum_type = UZLIB_CHKSUM_ADLER;
+       d->checksum = 1;
+
+       *wbits = (cmf >> 4) + 8;
+
+        return UZLIB_HEADER_ZLIB;
+    }
+}
diff --git a/lib/uzlib/tinfgzip.c b/lib/uzlib/tinfgzip.c
deleted file mode 100644
index 3b0feb5321..0000000000
--- a/lib/uzlib/tinfgzip.c
+++ /dev/null
@@ -1,110 +0,0 @@
-/*
- * uzlib  -  tiny deflate/inflate library (deflate, gzip, zlib)
- *
- * Copyright (c) 2003 by Joergen Ibsen / Jibz
- * All Rights Reserved
- *
- * http://www.ibsensoftware.com/
- *
- * Copyright (c) 2014-2018 by Paul Sokolovsky
- *
- * This software is provided 'as-is', without any express
- * or implied warranty.  In no event will the authors be
- * held liable for any damages arising from the use of
- * this software.
- *
- * Permission is granted to anyone to use this software
- * for any purpose, including commercial applications,
- * and to alter it and redistribute it freely, subject to
- * the following restrictions:
- *
- * 1. The origin of this software must not be
- *    misrepresented; you must not claim that you
- *    wrote the original software. If you use this
- *    software in a product, an acknowledgment in
- *    the product documentation would be appreciated
- *    but is not required.
- *
- * 2. Altered source versions must be plainly marked
- *    as such, and must not be misrepresented as
- *    being the original software.
- *
- * 3. This notice may not be removed or altered from
- *    any source distribution.
- */
-
-#include "uzlib.h"
-
-#define FTEXT    1
-#define FHCRC    2
-#define FEXTRA   4
-#define FNAME    8
-#define FCOMMENT 16
-
-void tinf_skip_bytes(uzlib_uncomp_t *d, int num);
-uint16_t tinf_get_uint16(uzlib_uncomp_t *d);
-
-void tinf_skip_bytes(uzlib_uncomp_t *d, int num)
-{
-    while (num--) uzlib_get_byte(d);
-}
-
-uint16_t tinf_get_uint16(uzlib_uncomp_t *d)
-{
-    unsigned int v = uzlib_get_byte(d);
-    v = (uzlib_get_byte(d) << 8) | v;
-    return v;
-}
-
-int uzlib_gzip_parse_header(uzlib_uncomp_t *d)
-{
-    unsigned char flg;
-
-    /* -- check format -- */
-
-    /* check id bytes */
-    if (uzlib_get_byte(d) != 0x1f || uzlib_get_byte(d) != 0x8b) return UZLIB_DATA_ERROR;
-
-    /* check method is deflate */
-    if (uzlib_get_byte(d) != 8) return UZLIB_DATA_ERROR;
-
-    /* get flag byte */
-    flg = uzlib_get_byte(d);
-
-    /* check that reserved bits are zero */
-    if (flg & 0xe0) return UZLIB_DATA_ERROR;
-
-    /* -- find start of compressed data -- */
-
-    /* skip rest of base header of 10 bytes */
-    tinf_skip_bytes(d, 6);
-
-    /* skip extra data if present */
-    if (flg & FEXTRA)
-    {
-       unsigned int xlen = tinf_get_uint16(d);
-       tinf_skip_bytes(d, xlen);
-    }
-
-    /* skip file name if present */
-    if (flg & FNAME) { while (uzlib_get_byte(d)); }
-
-    /* skip file comment if present */
-    if (flg & FCOMMENT) { while (uzlib_get_byte(d)); }
-
-    /* check header crc if present */
-    if (flg & FHCRC)
-    {
-       /*unsigned int hcrc =*/ tinf_get_uint16(d);
-
-        // TODO: Check!
-//       if (hcrc != (tinf_crc32(src, start - src) & 0x0000ffff))
-//          return UZLIB_DATA_ERROR;
-    }
-
-    /* initialize for crc32 checksum */
-    d->checksum_type = UZLIB_CHKSUM_CRC;
-    d->checksum = ~0;
-
-    return UZLIB_OK;
-}
diff --git a/lib/uzlib/tinfzlib.c b/lib/uzlib/tinfzlib.c
deleted file mode 100644
index 03954cefae..0000000000
--- a/lib/uzlib/tinfzlib.c
+++ /dev/null
@@ -1,66 +0,0 @@
-/*
- * uzlib  -  tiny deflate/inflate library (deflate, gzip, zlib)
- *
- * Copyright (c) 2003 by Joergen Ibsen / Jibz
- * All Rights Reserved
- *
- * http://www.ibsensoftware.com/
- *
- * Copyright (c) 2014-2018 by Paul Sokolovsky
- *
- * This software is provided 'as-is', without any express
- * or implied warranty.  In no event will the authors be
- * held liable for any damages arising from the use of
- * this software.
- *
- * Permission is granted to anyone to use this software
- * for any purpose, including commercial applications,
- * and to alter it and redistribute it freely, subject to
- * the following restrictions:
- *
- * 1. The origin of this software must not be
- *    misrepresented; you must not claim that you
- *    wrote the original software. If you use this
- *    software in a product, an acknowledgment in
- *    the product documentation would be appreciated
- *    but is not required.
- *
- * 2. Altered source versions must be plainly marked
- *    as such, and must not be misrepresented as
- *    being the original software.
- *
- * 3. This notice may not be removed or altered from
- *    any source distribution.
- */
-
-#include "uzlib.h"
-
-int uzlib_zlib_parse_header(uzlib_uncomp_t *d)
-{
-   unsigned char cmf, flg;
-
-   /* -- get header bytes -- */
-
-   cmf = uzlib_get_byte(d);
-   flg = uzlib_get_byte(d);
-
-   /* -- check format -- */
-
-   /* check checksum */
-   if ((256*cmf + flg) % 31) return UZLIB_DATA_ERROR;
-
-   /* check method is deflate */
-   if ((cmf & 0x0f) != 8) return UZLIB_DATA_ERROR;
-
-   /* check window size is valid */
-   if ((cmf >> 4) > 7) return UZLIB_DATA_ERROR;
-
-   /* check there is no preset dictionary */
-   if (flg & 0x20) return UZLIB_DATA_ERROR;
-
-   /* initialize for adler32 checksum */
-   d->checksum_type = UZLIB_CHKSUM_ADLER;
-   d->checksum = 1;
-
-   return cmf >> 4;
-}
diff --git a/lib/uzlib/uzlib.h b/lib/uzlib/uzlib.h
index ca58299fc3..3756ea7539 100644
--- a/lib/uzlib/uzlib.h
+++ b/lib/uzlib/uzlib.h
@@ -130,8 +130,9 @@ void uzlib_uncompress_init(uzlib_uncomp_t *d, void *dict, unsigned int dictLen);
 int  uzlib_uncompress(uzlib_uncomp_t *d);
 int  uzlib_uncompress_chksum(uzlib_uncomp_t *d);
 
-int uzlib_zlib_parse_header(uzlib_uncomp_t *d);
-int uzlib_gzip_parse_header(uzlib_uncomp_t *d);
+#define UZLIB_HEADER_ZLIB             0
+#define UZLIB_HEADER_GZIP             1
+int uzlib_parse_zlib_gzip_header(uzlib_uncomp_t *d, int *wbits);
 
 /* Compression API */
 
diff --git a/ports/stm32/mboot/Makefile b/ports/stm32/mboot/Makefile
index 1f6ba063b2..630327d700 100755
--- a/ports/stm32/mboot/Makefile
+++ b/ports/stm32/mboot/Makefile
@@ -105,7 +105,7 @@ LIB_SRC_C += \
 	lib/oofatfs/ffunicode.c \
 	lib/uzlib/adler32.c \
 	lib/uzlib/crc32.c \
-	lib/uzlib/tinfgzip.c \
+	lib/uzlib/header.c \
 	lib/uzlib/tinflate.c
 
 SRC_C += \
diff --git a/ports/stm32/mboot/gzstream.c b/ports/stm32/mboot/gzstream.c
index f008eca5cd..764ef0a477 100644
--- a/ports/stm32/mboot/gzstream.c
+++ b/ports/stm32/mboot/gzstream.c
@@ -78,8 +78,9 @@ int gz_stream_init_from_stream(void *stream_data, stream_read_t stream_read) {
     memset(&gz_stream.decomp, 0, sizeof(gz_stream.decomp));
     gz_stream.decomp.source_read_cb = gz_stream_read_src;
 
-    int st = uzlib_gzip_parse_header(&gz_stream.decomp);
-    if (st != UZLIB_OK) {
+    int header_wbits;
+    int st = uzlib_parse_zlib_gzip_header(&gz_stream.decomp, &header_wbits);
+    if (st != UZLIB_HEADER_GZIP) {
         return -MBOOT_ERRNO_GUNZIP_FAILED;
     }