diff --git a/module/lua/lfunc.h b/module/lua/lfunc.h
index 59a4fa75c4..638971bdd0 100644
--- a/module/lua/lfunc.h
+++ b/module/lua/lfunc.h
@@ -13,10 +13,10 @@
 
 
 #define sizeCclosure(n)	(cast(int, sizeof(CClosure)) + \
-                         cast(int, sizeof(TValue)*((n)-1)))
+                         cast(int, sizeof(TValue)*((n))))
 
 #define sizeLclosure(n)	(cast(int, sizeof(LClosure)) + \
-                         cast(int, sizeof(TValue *)*((n)-1)))
+                         cast(int, sizeof(TValue *)*((n))))
 
 
 LUAI_FUNC Proto *luaF_newproto (lua_State *L);
diff --git a/module/lua/lobject.h b/module/lua/lobject.h
index a16b8d62eb..ede697cfc5 100644
--- a/module/lua/lobject.h
+++ b/module/lua/lobject.h
@@ -514,14 +514,14 @@ typedef struct UpVal {
 typedef struct CClosure {
   ClosureHeader;
   lua_CFunction f;
-  TValue upvalue[1];  /* list of upvalues */
+  TValue upvalue[];  /* list of upvalues */
 } CClosure;
 
 
 typedef struct LClosure {
   ClosureHeader;
   struct Proto *p;
-  UpVal *upvals[1];  /* list of upvalues */
+  UpVal *upvals[];  /* list of upvalues */
 } LClosure;
 
 
diff --git a/module/os/freebsd/zfs/zfs_debug.c b/module/os/freebsd/zfs/zfs_debug.c
index dad342b06f..b75cf09218 100644
--- a/module/os/freebsd/zfs/zfs_debug.c
+++ b/module/os/freebsd/zfs/zfs_debug.c
@@ -30,7 +30,7 @@ typedef struct zfs_dbgmsg {
 	list_node_t zdm_node;
 	time_t zdm_timestamp;
 	int zdm_size;
-	char zdm_msg[1]; /* variable length allocation */
+	char zdm_msg[];
 } zfs_dbgmsg_t;
 
 list_t zfs_dbgmsgs;
@@ -159,7 +159,7 @@ __zfs_dbgmsg(char *buf)
 
 	DTRACE_PROBE1(zfs__dbgmsg, char *, buf);
 
-	size = sizeof (zfs_dbgmsg_t) + strlen(buf);
+	size = sizeof (zfs_dbgmsg_t) + strlen(buf) + 1;
 	zdm = kmem_zalloc(size, KM_SLEEP);
 	zdm->zdm_size = size;
 	zdm->zdm_timestamp = gethrestime_sec();
diff --git a/module/os/linux/zfs/zfs_debug.c b/module/os/linux/zfs/zfs_debug.c
index 98c9923d59..5958063731 100644
--- a/module/os/linux/zfs/zfs_debug.c
+++ b/module/os/linux/zfs/zfs_debug.c
@@ -30,7 +30,7 @@ typedef struct zfs_dbgmsg {
 	procfs_list_node_t	zdm_node;
 	uint64_t		zdm_timestamp;
 	int			zdm_size;
-	char			zdm_msg[1]; /* variable length allocation */
+	char			zdm_msg[]; /* variable length allocation */
 } zfs_dbgmsg_t;
 
 procfs_list_t zfs_dbgmsgs;
@@ -134,7 +134,7 @@ __set_error(const char *file, const char *func, int line, int err)
 void
 __zfs_dbgmsg(char *buf)
 {
-	int size = sizeof (zfs_dbgmsg_t) + strlen(buf);
+	int size = sizeof (zfs_dbgmsg_t) + strlen(buf) + 1;
 	zfs_dbgmsg_t *zdm = kmem_zalloc(size, KM_SLEEP);
 	zdm->zdm_size = size;
 	zdm->zdm_timestamp = gethrestime_sec();
diff --git a/module/zfs/vdev_indirect.c b/module/zfs/vdev_indirect.c
index 8762855d46..9e4c115f21 100644
--- a/module/zfs/vdev_indirect.c
+++ b/module/zfs/vdev_indirect.c
@@ -270,7 +270,7 @@ typedef struct indirect_split {
 	 */
 	indirect_child_t *is_good_child;
 
-	indirect_child_t is_child[1]; /* variable-length */
+	indirect_child_t is_child[];
 } indirect_split_t;
 
 /*