diff --git a/src/os/unix/ngx_shmem.c b/src/os/unix/ngx_shmem.c
index 3ec7cbf1f..e5dd6ad88 100644
--- a/src/os/unix/ngx_shmem.c
+++ b/src/os/unix/ngx_shmem.c
@@ -19,6 +19,7 @@ ngx_shm_alloc(ngx_shm_t *shm)
                                 MAP_ANON|MAP_SHARED, -1, 0);
 
     if (shm->addr == MAP_FAILED) {
+        shm->addr = NULL;
         ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                       "mmap(MAP_ANON|MAP_SHARED, %uz) failed", shm->size);
         return NGX_ERROR;
@@ -35,6 +36,8 @@ ngx_shm_free(ngx_shm_t *shm)
         ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                       "munmap(%p, %uz) failed", shm->addr, shm->size);
     }
+
+    shm->addr = NULL;
 }
 
 #elif (NGX_HAVE_MAP_DEVZERO)
@@ -56,6 +59,7 @@ ngx_shm_alloc(ngx_shm_t *shm)
                                 MAP_SHARED, fd, 0);
 
     if (shm->addr == MAP_FAILED) {
+        shm->addr = NULL;
         ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                       "mmap(/dev/zero, MAP_SHARED, %uz) failed", shm->size);
     }
@@ -65,7 +69,7 @@ ngx_shm_alloc(ngx_shm_t *shm)
                       "close(\"/dev/zero\") failed");
     }
 
-    return (shm->addr == MAP_FAILED) ? NGX_ERROR : NGX_OK;
+    return (shm->addr == NULL) ? NGX_ERROR : NGX_OK;
 }
 
 
@@ -76,6 +80,8 @@ ngx_shm_free(ngx_shm_t *shm)
         ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                       "munmap(%p, %uz) failed", shm->addr, shm->size);
     }
+
+    shm->addr = NULL;
 }
 
 #elif (NGX_HAVE_SYSVSHM)
@@ -102,6 +108,7 @@ ngx_shm_alloc(ngx_shm_t *shm)
     shm->addr = shmat(id, NULL, 0);
 
     if (shm->addr == (void *) -1) {
+        shm->addr = NULL;
         ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno, "shmat() failed");
     }
 
@@ -110,7 +117,7 @@ ngx_shm_alloc(ngx_shm_t *shm)
                       "shmctl(IPC_RMID) failed");
     }
 
-    return (shm->addr == (void *) -1) ? NGX_ERROR : NGX_OK;
+    return (shm->addr == NULL) ? NGX_ERROR : NGX_OK;
 }
 
 
@@ -121,6 +128,8 @@ ngx_shm_free(ngx_shm_t *shm)
         ngx_log_error(NGX_LOG_ALERT, shm->log, ngx_errno,
                       "shmdt(%p) failed", shm->addr);
     }
+
+    shm->addr = NULL;
 }
 
 #endif
diff --git a/src/os/win32/ngx_shmem.c b/src/os/win32/ngx_shmem.c
index c3ed699f7..df1166ee6 100644
--- a/src/os/win32/ngx_shmem.c
+++ b/src/os/win32/ngx_shmem.c
@@ -158,4 +158,6 @@ ngx_shm_free(ngx_shm_t *shm)
                       "CloseHandle() of file mapping \"%V\" failed",
                       &shm->name);
     }
+
+    shm->addr = NULL;
 }