Index: ext/zlib/zlib.c
===================================================================
--- ext/zlib/zlib.c	(revision 36146)
+++ ext/zlib/zlib.c	(working copy)
@@ -72,6 +72,7 @@ static void finalizer_warn(const char*);
 
 struct zstream;
 struct zstream_funcs;
+struct zstream_run_args;
 static void zstream_init(struct zstream*, const struct zstream_funcs*);
 static void zstream_expand_buffer(struct zstream*);
 static void zstream_expand_buffer_into(struct zstream*, unsigned long);
@@ -557,13 +558,17 @@ struct zstream {
 #define ZSTREAM_AVAIL_OUT_STEP_MIN    2048
 
 static const struct zstream_funcs deflate_funcs = {
-    deflateReset, deflateEnd, deflate,
+    deflateReset, deflateEnd, deflate
 };
 
 static const struct zstream_funcs inflate_funcs = {
-    inflateReset, inflateEnd, inflate,
+    inflateReset, inflateEnd, inflate
 };
 
+struct zstream_run_args {
+    struct zstream * z;
+    int flush;
+};
 
 static voidpf
 zlib_mem_alloc(voidpf opaque, uInt items, uInt size)
@@ -871,13 +876,37 @@ zstream_end(struct zstream *z)
     return Qnil;
 }
 
+static VALUE
+zstream_run_func(void *ptr) {
+    struct zstream_run_args *args = (struct zstream_run_args *)ptr;
+    int err, flush = args->flush;
+    struct zstream *z = args->z;
+    uInt n;
+
+    n = z->stream.avail_out;
+    err = z->func->run(&z->stream, flush);
+    z->buf_filled += n - z->stream.avail_out;
+
+    return (VALUE)err;
+}
+
+/*
+ * There is no safe way to interrupt z->run->func().
+ */
+static void
+zstream_unblock_func(void *ptr) {
+}
+
 static void
 zstream_run(struct zstream *z, Bytef *src, long len, int flush)
 {
-    uInt n;
+    struct zstream_run_args args;
     int err;
     volatile VALUE guard = Qnil;
 
+    args.z = z;
+    args.flush = flush;
+
     if (NIL_P(z->input) && len == 0) {
 	z->stream.next_in = (Bytef*)"";
 	z->stream.avail_in = 0;
@@ -900,10 +929,10 @@ zstream_run(struct zstream *z, Bytef *sr
 	/* VC allocates err and guard to same address.  accessing err and guard
 	   in same scope prevents it. */
 	RB_GC_GUARD(guard);
-	n = z->stream.avail_out;
-	err = z->func->run(&z->stream, flush);
-	z->buf_filled += n - z->stream.avail_out;
-	rb_thread_schedule();
+
+	err = (int)rb_thread_blocking_region(
+		zstream_run_func, (void *)&args,
+		zstream_unblock_func, NULL);
 
 	if (err == Z_STREAM_END) {
 	    z->flags &= ~ZSTREAM_FLAG_IN_STREAM;