diff --git a/libraries/pack200/src/unpack.h b/libraries/pack200/src/unpack.h
index 8363740d..cc5dd60a 100644
--- a/libraries/pack200/src/unpack.h
+++ b/libraries/pack200/src/unpack.h
@@ -23,6 +23,8 @@
  * questions.
  */
 
+#pragma once
+
 // Global Structures
 struct jar;
 struct gunzip;
@@ -33,6 +35,8 @@ struct cpindex;
 struct inner_class;
 struct value_stream;
 
+typedef int64_t (*read_input_fn_t)(unpacker *self, void *buf, int64_t minlen, int64_t maxlen);
+
 struct cpindex
 {
     uint32_t len;
@@ -186,8 +190,6 @@ struct unpacker
     int unsized_bytes_read;
 
     // callback to read at least one byte, up to available input
-    typedef int64_t (*read_input_fn_t)(unpacker *self, void *buf, int64_t minlen,
-                                       int64_t maxlen);
     read_input_fn_t read_input_fn;
 
     // archive header fields
diff --git a/libraries/pack200/src/zip.cpp b/libraries/pack200/src/zip.cpp
index 13b955cc..e776510b 100644
--- a/libraries/pack200/src/zip.cpp
+++ b/libraries/pack200/src/zip.cpp
@@ -444,7 +444,7 @@ static int64_t read_input_via_gzip(unpacker *u, void *buf, int64_t minlen, int64
     char *bufptr = (char *)buf;
     char *inbuf = u->gzin->inbuf;
     size_t inbuflen = sizeof(u->gzin->inbuf);
-    unpacker::read_input_fn_t read_gzin_fn = (unpacker::read_input_fn_t)u->gzin->read_input_fn;
+    read_input_fn_t read_gzin_fn = u->gzin->read_input_fn;
     z_stream &zs = *(z_stream *)u->gzin->zstream;
     while (numread < minlen)
     {
@@ -507,7 +507,7 @@ void gunzip::init(unpacker *u_)
     BYTES_OF(*this).clear();
     u = u_;
     assert(u->gzin == nullptr); // once only, please
-    read_input_fn = (void *)u->read_input_fn;
+    read_input_fn = u->read_input_fn;
     zstream = NEW(z_stream, 1);
     u->gzin = this;
     u->read_input_fn = read_input_via_gzip;
@@ -574,7 +574,7 @@ void gunzip::free()
 {
     assert(u->gzin == this);
     u->gzin = nullptr;
-    u->read_input_fn = (unpacker::read_input_fn_t) this->read_input_fn;
+    u->read_input_fn = this->read_input_fn;
     inflateEnd((z_stream *)zstream);
     ::free(zstream);
     zstream = nullptr;
@@ -583,7 +583,7 @@ void gunzip::free()
 
 void gunzip::read_fixed_field(char *buf, size_t buflen)
 {
-    int64_t nr = ((unpacker::read_input_fn_t)read_input_fn)(u, buf, buflen, buflen);
+    int64_t nr = read_input_fn(u, buf, buflen, buflen);
     if ((size_t)nr != buflen)
         unpack_abort("short stream header");
 }
diff --git a/libraries/pack200/src/zip.h b/libraries/pack200/src/zip.h
index 5fcbae94..ff973a86 100644
--- a/libraries/pack200/src/zip.h
+++ b/libraries/pack200/src/zip.h
@@ -22,12 +22,14 @@
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */
+#pragma once
+
 #include <stdint.h>
 typedef unsigned short ushort;
 typedef unsigned int uint32_t;
 typedef unsigned char uchar;
 
-struct unpacker;
+#include "unpack.h"
 
 struct jar
 {
@@ -95,7 +97,7 @@ struct gunzip
     // pointer to outer unpacker, for error checks etc.
     unpacker *u;
 
-    void *read_input_fn; // underlying \bchar\b stream
+    read_input_fn_t read_input_fn; // underlying \bchar\b stream
     void *zstream;       // inflater state
     char inbuf[1 << 14]; // input buffer