diff --git a/libc/bionic/pthread_attr.cpp b/libc/bionic/pthread_attr.cpp
index fe1ed4a..d7c6c13 100644
--- a/libc/bionic/pthread_attr.cpp
+++ b/libc/bionic/pthread_attr.cpp
@@ -30,12 +30,16 @@
 
 #include "pthread_internal.h"
 
-#define DEFAULT_STACK_SIZE (1024 * 1024)
+// Traditionally we give threads a 1MiB stack. When we started allocating per-thread
+// alternate signal stacks to ease debugging of stack overflows, we subtracted the
+// same amount we were using there from the default thread stack size. This should
+// keep memory usage roughly constant.
+#define DEFAULT_THREAD_STACK_SIZE ((1 * 1024 * 1024) - SIGSTKSZ)
 
 int pthread_attr_init(pthread_attr_t* attr) {
   attr->flags = 0;
   attr->stack_base = NULL;
-  attr->stack_size = DEFAULT_STACK_SIZE;
+  attr->stack_size = DEFAULT_THREAD_STACK_SIZE;
   attr->guard_size = PAGE_SIZE;
   attr->sched_policy = SCHED_NORMAL;
   attr->sched_priority = 0;