diff --git a/libc/include/errno.h b/libc/include/errno.h
index 2e5ce5f..1a36b7a 100644
--- a/libc/include/errno.h
+++ b/libc/include/errno.h
@@ -41,7 +41,7 @@
 #endif
 
 /* internal function returning the address of the thread-specific errno */
-extern volatile int*   __errno(void);
+extern volatile int* __errno(void) __pure2;
 
 /* a macro expanding to the errno l-value */
 #define  errno   (*__errno())
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 5c9b626..29caafc 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -226,7 +226,7 @@
 int pthread_rwlock_unlock(pthread_rwlock_t *rwlock) __nonnull((1));
 int pthread_rwlock_wrlock(pthread_rwlock_t*) __nonnull((1));
 
-pthread_t pthread_self(void);
+pthread_t pthread_self(void) __pure2;
 
 int pthread_setname_np(pthread_t, const char*) __nonnull((2));
 
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index 483aaf0..0f862c3 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -138,21 +138,21 @@
     int  rem;
 } div_t;
 
-extern div_t   div(int, int);
+extern div_t   div(int, int) __pure2;
 
 typedef struct {
     long int  quot;
     long int  rem;
 } ldiv_t;
 
-extern ldiv_t   ldiv(long, long);
+extern ldiv_t   ldiv(long, long) __pure2;
 
 typedef struct {
     long long int  quot;
     long long int  rem;
 } lldiv_t;
 
-extern lldiv_t   lldiv(long long, long long);
+extern lldiv_t   lldiv(long long, long long) __pure2;
 
 /* BSD compatibility. */
 extern const char* getprogname(void);
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index b4982cb..ee6d7b1 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -54,7 +54,7 @@
 extern pid_t  fork(void);
 extern pid_t  vfork(void);
 extern pid_t  getpid(void);
-extern pid_t  gettid(void);
+extern pid_t  gettid(void) __pure2;
 extern pid_t  getpgid(pid_t);
 extern int    setpgid(pid_t, pid_t);
 extern pid_t  getppid(void);