diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 7b6cc4e..c1a9626 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -720,17 +720,15 @@ zstream_expand_buffer_into(struct zstream *z, unsigned long size)
     }
 }
 
-static void *
-zstream_expand_buffer_protect(void *ptr)
+static int
+zstream_expand_buffer_protect(struct zstream *z)
 {
-    struct zstream *z = (struct zstream *)ptr;
     int state = 0;
 
     rb_protect((VALUE (*)(VALUE))zstream_expand_buffer, (VALUE)z, &state);
 
-    return (void *)(VALUE)state;
+    return state;
 }
-
 static int
 zstream_expand_buffer_non_stream(struct zstream *z)
 {
@@ -1023,57 +1021,14 @@ zstream_ensure_end(VALUE v)
 }
 
 static void *
-zstream_run_func(void *ptr)
+zstream_run_once(void *_arguments)
 {
-    struct zstream_run_args *args = (struct zstream_run_args *)ptr;
-    int err, state, flush = args->flush;
-    struct zstream *z = args->z;
-    uInt n;
-
-    err = Z_OK;
-    while (!args->interrupt) {
-	n = z->stream.avail_out;
-	err = z->func->run(&z->stream, flush);
-	rb_str_set_len(z->buf, ZSTREAM_BUF_FILLED(z) + (n - z->stream.avail_out));
-
-	if (err == Z_STREAM_END) {
-	    z->flags &= ~ZSTREAM_FLAG_IN_STREAM;
-	    z->flags |= ZSTREAM_FLAG_FINISHED;
-	    break;
-	}
-
-	if (err != Z_OK && err != Z_BUF_ERROR)
-	    break;
-
-	if (z->stream.avail_out > 0) {
-	    z->flags |= ZSTREAM_FLAG_IN_STREAM;
-	    break;
-	}
-
-	if (z->stream.avail_in == 0 && z->func == &inflate_funcs) {
-	    /* break here because inflate() return Z_BUF_ERROR when avail_in == 0. */
-	    /* but deflate() could be called with avail_in == 0 (there's hidden buffer
-	       in zstream->state) */
-	    z->flags |= ZSTREAM_FLAG_IN_STREAM;
-	    break;
-	}
+    struct zstream_run_args *arguments = (struct zstream_run_args *)_arguments;
+    struct zstream *z = arguments->z;
 
-	if (args->stream_output) {
-	    state = (int)(VALUE)rb_thread_call_with_gvl(zstream_expand_buffer_protect,
-							(void *)z);
-	}
-	else {
-	    state = zstream_expand_buffer_non_stream(z);
-	}
+    uintptr_t error = z->func->run(&z->stream, arguments->flush);
 
-	if (state) {
-	    err = Z_OK; /* buffer expanded but stream processing was stopped */
-	    args->jump_state = state;
-	    break;
-	}
-    }
-
-    return (void *)(VALUE)err;
+    return (void*)error;
 }
 
 /*
@@ -1088,6 +1043,63 @@ zstream_unblock_func(void *ptr)
     args->interrupt = 1;
 }
 
+static int zstream_run_func(struct zstream_run_args *args)
+{
+    struct zstream *z = args->z;
+
+    int err = Z_OK;
+    int state;
+
+    while (!args->interrupt) {
+        uInt n = z->stream.avail_out;
+
+#ifndef RB_NOGVL_UBF_ASYNC_SAFE
+        err = (int)(VALUE)rb_thread_call_without_gvl(zstream_run_once, (void *)args, zstream_unblock_func, (void *)args);
+#else
+        err = (int)(VALUE)rb_nogvl(zstream_run_once, (void *)args, zstream_unblock_func, (void *)args, RB_NOGVL_UBF_ASYNC_SAFE);
+#endif
+
+        rb_str_set_len(z->buf, ZSTREAM_BUF_FILLED(z) + (n - z->stream.avail_out));
+
+        if (err == Z_STREAM_END) {
+            z->flags &= ~ZSTREAM_FLAG_IN_STREAM;
+            z->flags |= ZSTREAM_FLAG_FINISHED;
+            break;
+        }
+
+        if (err != Z_OK && err != Z_BUF_ERROR)
+            break;
+
+        if (z->stream.avail_out > 0) {
+            z->flags |= ZSTREAM_FLAG_IN_STREAM;
+            break;
+        }
+
+        if (z->stream.avail_in == 0 && z->func == &inflate_funcs) {
+            /* break here because inflate() return Z_BUF_ERROR when avail_in == 0. */
+            /* but deflate() could be called with avail_in == 0 (there's hidden buffer
+                in zstream->state) */
+            z->flags |= ZSTREAM_FLAG_IN_STREAM;
+            break;
+        }
+
+        if (args->stream_output) {
+            state = zstream_expand_buffer_protect(z);
+        }
+        else {
+            state = zstream_expand_buffer_non_stream(z);
+        }
+
+        if (state) {
+            err = Z_OK;
+            args->jump_state = state;
+            break;
+        }
+    }
+
+    return err;
+}
+
 static VALUE
 zstream_run_try(VALUE value_arg)
 {
@@ -1097,7 +1109,6 @@ zstream_run_try(VALUE value_arg)
     long len = args->len;
     int flush = args->flush;
 
-    int err;
     VALUE old_input = Qnil;
 
     /* Cannot start zstream while it is in progress. */
@@ -1126,14 +1137,7 @@ zstream_run_try(VALUE value_arg)
     }
 
 loop:
-#ifndef RB_NOGVL_UBF_ASYNC_SAFE
-    err = (int)(VALUE)rb_thread_call_without_gvl(zstream_run_func, (void *)args,
-						 zstream_unblock_func, (void *)args);
-#else
-    err = (int)(VALUE)rb_nogvl(zstream_run_func, (void *)args,
-                               zstream_unblock_func, (void *)args,
-                               RB_NOGVL_UBF_ASYNC_SAFE);
-#endif
+    int err = zstream_run_func(args);
 
     /* retry if no exception is thrown */
     if (err == Z_OK && args->interrupt) {