diff --git a/src/os/unix/ngx_darwin_init.c b/src/os/unix/ngx_darwin_init.c
index 70748ee57..0f5a8bb06 100644
--- a/src/os/unix/ngx_darwin_init.c
+++ b/src/os/unix/ngx_darwin_init.c
@@ -115,7 +115,8 @@ ngx_os_specific_init(ngx_log_t *log)
                 return NGX_ERROR;
             }
 
-            ngx_darwin_kern_ostype[size - 1] = '\0';
+            ngx_darwin_kern_ostype[sizeof(ngx_darwin_kern_ostype) - 1]
+                = '\0';
         }
     }
 
@@ -135,7 +136,8 @@ ngx_os_specific_init(ngx_log_t *log)
                 return NGX_ERROR;
             }
 
-            ngx_darwin_kern_osrelease[size - 1] = '\0';
+            ngx_darwin_kern_osrelease[sizeof(ngx_darwin_kern_osrelease) - 1]
+                = '\0';
         }
     }
 
diff --git a/src/os/unix/ngx_freebsd_init.c b/src/os/unix/ngx_freebsd_init.c
index f732637d1..598181691 100644
--- a/src/os/unix/ngx_freebsd_init.c
+++ b/src/os/unix/ngx_freebsd_init.c
@@ -116,7 +116,8 @@ ngx_os_specific_init(ngx_log_t *log)
             return NGX_ERROR;
         }
 
-        ngx_freebsd_kern_ostype[size - 1] = '\0';
+        ngx_freebsd_kern_ostype[sizeof(ngx_freebsd_kern_ostype) - 1]
+            = '\0';
     }
 
     size = sizeof(ngx_freebsd_kern_osrelease);
@@ -129,7 +130,8 @@ ngx_os_specific_init(ngx_log_t *log)
             return NGX_ERROR;
         }
 
-        ngx_freebsd_kern_osrelease[size - 1] = '\0';
+        ngx_freebsd_kern_osrelease[sizeof(ngx_freebsd_kern_osrelease) - 1]
+            = '\0';
     }