diff --git a/Misc/NEWS.d/next/Library/2018-06-21-11-35-47.bpo-33916.cZgPCD.rst b/Misc/NEWS.d/next/Library/2018-06-21-11-35-47.bpo-33916.cZgPCD.rst
new file mode 100644
index 00000000000000..65b9d2bf89a588
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-06-21-11-35-47.bpo-33916.cZgPCD.rst
@@ -0,0 +1,2 @@
+bz2 and lzma: When Decompressor.__init__() is called twice, free the old
+lock to not leak memory.
diff --git a/Modules/_bz2module.c b/Modules/_bz2module.c
index 0789b6179e52be..3890b60b1b87b3 100644
--- a/Modules/_bz2module.c
+++ b/Modules/_bz2module.c
@@ -634,11 +634,15 @@ _bz2_BZ2Decompressor___init___impl(BZ2Decompressor *self)
 {
     int bzerror;
 
-    self->lock = PyThread_allocate_lock();
-    if (self->lock == NULL) {
+    PyThread_type_lock lock = PyThread_allocate_lock();
+    if (lock == NULL) {
         PyErr_SetString(PyExc_MemoryError, "Unable to allocate lock");
         return -1;
     }
+    if (self->lock != NULL) {
+        PyThread_free_lock(self->lock);
+    }
+    self->lock = lock;
 
     self->needs_input = 1;
     self->bzs_avail_in_real = 0;
diff --git a/Modules/_lzmamodule.c b/Modules/_lzmamodule.c
index 5bcd088d772188..7b501d8202d8b9 100644
--- a/Modules/_lzmamodule.c
+++ b/Modules/_lzmamodule.c
@@ -1163,11 +1163,15 @@ _lzma_LZMADecompressor___init___impl(Decompressor *self, int format,
     self->lzs.allocator = &self->alloc;
     self->lzs.next_in = NULL;
 
-    self->lock = PyThread_allocate_lock();
-    if (self->lock == NULL) {
+    PyThread_type_lock lock = PyThread_allocate_lock();
+    if (lock == NULL) {
         PyErr_SetString(PyExc_MemoryError, "Unable to allocate lock");
         return -1;
     }
+    if (self->lock != NULL) {
+        PyThread_free_lock(self->lock);
+    }
+    self->lock = lock;
 
     self->check = LZMA_CHECK_UNKNOWN;
     self->needs_input = 1;