Modules/zlibmodule.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index 480bc1ca2a..f904f992af 100644
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -85,10 +85,12 @@ Buffer_OnError(_BlocksOutputBuffer *buffer)
 }
 
 
-#define ENTER_ZLIB(obj) \
-    Py_BEGIN_ALLOW_THREADS; \
-    PyThread_acquire_lock((obj)->lock, 1); \
-    Py_END_ALLOW_THREADS;
+#define ENTER_ZLIB(obj) do {                      \
+    if (!PyThread_acquire_lock((obj)->lock, 0)) { \
+        Py_BEGIN_ALLOW_THREADS                    \
+        PyThread_acquire_lock((obj)->lock, 1);    \
+        Py_END_ALLOW_THREADS                      \
+    } } while (0)
 #define LEAVE_ZLIB(obj) PyThread_release_lock((obj)->lock);
 
 #if defined(ZLIB_VERNUM) && ZLIB_VERNUM >= 0x1221
@@ -670,14 +672,13 @@ zlib_Compress_compress_impl(compobject *self, PyTypeObject *cls,
     PyObject *RetVal;
     int err;
     _BlocksOutputBuffer buffer = {.list = NULL};
-
     zlibstate *state = PyType_GetModuleState(cls);
 
+    ENTER_ZLIB(self);
+
     self->zst.next_in = data->buf;
     Py_ssize_t ibuflen = data->len;
 
-    ENTER_ZLIB(self);
-
     if (Buffer_InitAndGrow(&buffer, -1, &self->zst.next_out, &self->zst.avail_out) < 0) {
         goto error;
     }
@@ -803,11 +804,11 @@ zlib_Decompress_decompress_impl(compobject *self, PyTypeObject *cls,
     } else if (max_length == 0)
         max_length = -1;
 
+    ENTER_ZLIB(self);
+
     self->zst.next_in = data->buf;
     ibuflen = data->len;
 
-    ENTER_ZLIB(self);
-
     if (Buffer_InitAndGrow(&buffer, max_length, &self->zst.next_out, &self->zst.avail_out) < 0) {
         goto abort;
     }