diff --git a/lfs3.c b/lfs3.c
index 87ac2bae..6f2d7eb3 100644
--- a/lfs3.c
+++ b/lfs3.c
@@ -9783,6 +9783,13 @@ enum lfs3_tstate {
     LFS3_TSTATE_DONE        = 8,
 };
 
+// tortoise for cycle detection
+typedef struct lfs3_mtortoise {
+    lfs3_block_t blocks[2];
+    lfs3_block_t dist;
+    uint8_t power;
+} lfs3_mtortoise_t;
+
 static void lfs3_trv_init(lfs3_trv_t *trv, uint32_t flags) {
     trv->b.h.flags = lfs3_o_typeflags(LFS3_type_TRV)
             | lfs3_t_tstateflags(LFS3_TSTATE_MROOTANCHOR)
@@ -9792,11 +9799,15 @@ static void lfs3_trv_init(lfs3_trv_t *trv, uint32_t flags) {
     trv->b.h.mdir.r.blocks[0] = -1;
     trv->b.h.mdir.r.blocks[1] = -1;
     lfs3_bshrub_init(&trv->b);
+    // bit of a hack, but we reuse the shrub's leaf as a tortoise for
+    // cycle detection to save memory, see lfs3_mtree_traverse_
+    lfs3_mtortoise_t *mtortoise = (lfs3_mtortoise_t*)&trv->b.shrub.leaf.r;
+    LFS3_ASSERT(sizeof(lfs3_mtortoise_t) <= sizeof(trv->b.shrub.leaf.r));
+    mtortoise->blocks[0] = -1;
+    mtortoise->blocks[1] = -1;
+    mtortoise->dist = 0;
+    mtortoise->power = 0;
     trv->h = NULL;
-    trv->u.mtortoise.blocks[0] = -1;
-    trv->u.mtortoise.blocks[1] = -1;
-    trv->u.mtortoise.step = 0;
-    trv->u.mtortoise.power = 0;
     trv->gcksum = 0;
 }
 
@@ -9859,22 +9870,26 @@ static lfs3_stag_t lfs3_mtree_traverse_(lfs3_t *lfs3, lfs3_trv_t *trv,
                 // btree inner nodes require checksums of their pointers,
                 // so creating a valid cycle is actually quite difficult
                 //
+                // a bit of a hack, but we reuse the shrub's leaf as a
+                // tortoise to save memory
+                lfs3_mtortoise_t *mtortoise
+                        = (lfs3_mtortoise_t*)&trv->b.shrub.leaf.r;
                 if (lfs3_mptr_cmp(
                         trv->b.h.mdir.r.blocks,
-                        trv->u.mtortoise.blocks) == 0) {
+                        mtortoise->blocks) == 0) {
                     LFS3_ERROR("Cycle detected during mtree traversal "
                                 "0x{%"PRIx32",%"PRIx32"}",
                             trv->b.h.mdir.r.blocks[0],
                             trv->b.h.mdir.r.blocks[1]);
                     return LFS3_ERR_CORRUPT;
                 }
-                if (trv->u.mtortoise.step == (1U << trv->u.mtortoise.power)) {
-                    trv->u.mtortoise.blocks[0] = trv->b.h.mdir.r.blocks[0];
-                    trv->u.mtortoise.blocks[1] = trv->b.h.mdir.r.blocks[1];
-                    trv->u.mtortoise.step = 0;
-                    trv->u.mtortoise.power += 1;
+                if (mtortoise->dist == (1U << mtortoise->power)) {
+                    mtortoise->blocks[0] = trv->b.h.mdir.r.blocks[0];
+                    mtortoise->blocks[1] = trv->b.h.mdir.r.blocks[1];
+                    mtortoise->dist = 0;
+                    mtortoise->power += 1;
                 }
-                trv->u.mtortoise.step += 1;
+                mtortoise->dist += 1;
 
                 bptr_->d.u.buffer = (const uint8_t*)&trv->b.h.mdir;
                 return LFS3_TAG_MDIR;
@@ -9889,7 +9904,7 @@ static lfs3_stag_t lfs3_mtree_traverse_(lfs3_t *lfs3, lfs3_trv_t *trv,
                 }
 
                 // transition to traversing the mtree
-                trv->u.bid = -2;
+                trv->bid = -2;
                 lfs3_t_settstate(&trv->b.h.flags, LFS3_TSTATE_MTREE);
                 continue;
 
@@ -9945,7 +9960,7 @@ static lfs3_stag_t lfs3_mtree_traverse_(lfs3_t *lfs3, lfs3_trv_t *trv,
             // here, lfs3_bshrub_fetch ignores these for us
             if (err != LFS3_ERR_NOENT) {
                 // start traversing
-                trv->u.bid = -2;
+                trv->bid = -2;
                 lfs3_t_settstate(&trv->b.h.flags, LFS3_TSTATE_BTREE);
                 continue;
 
@@ -9990,7 +10005,7 @@ static lfs3_stag_t lfs3_mtree_traverse_(lfs3_t *lfs3, lfs3_trv_t *trv,
             // transition to traversing the file
             const lfs3_file_t *file = (const lfs3_file_t*)trv->h;
             trv->b.shrub = file->b.shrub;
-            trv->u.bid = -2;
+            trv->bid = -2;
             lfs3_t_settstate(&trv->b.h.flags, LFS3_TSTATE_HBTREE);
             continue;
         #endif
@@ -10002,8 +10017,8 @@ static lfs3_stag_t lfs3_mtree_traverse_(lfs3_t *lfs3, lfs3_trv_t *trv,
         case LFS3_TSTATE_BTREE:;
         case LFS3_TSTATE_HBTREE:;
             // traverse through our bshrub/btree
-            tag = lfs3_bshrub_traverse(lfs3, &trv->b, trv->u.bid+1,
-                    &trv->u.bid, NULL, &data);
+            tag = lfs3_bshrub_traverse(lfs3, &trv->b, trv->bid+1,
+                    &trv->bid, NULL, &data);
             if (tag < 0) {
                 if (tag == LFS3_ERR_NOENT) {
                     // clear the bshrub state
diff --git a/lfs3.h b/lfs3.h
index 3eed2892..881309fd 100644
--- a/lfs3.h
+++ b/lfs3.h
@@ -771,20 +771,12 @@ typedef struct lfs3_dir {
 // littlefs traversal type
 typedef struct lfs3_trv {
     // mdir/bshrub/btree state, this also includes our traversal
-    // state machine
+    // state machine and cycle detection state
     lfs3_bshrub_t b;
     // opened file state
     lfs3_handle_t *h;
-    union {
-        // cycle detection state, only valid when traversing the mroot chain
-        struct {
-            lfs3_block_t blocks[2];
-            lfs3_block_t step;
-            uint8_t power;
-        } mtortoise;
-        // btree traversal state
-        lfs3_sbid_t bid;
-    } u;
+    // bshrub/btree traversal state
+    lfs3_sbid_t bid;
 
     // recalculate gcksum when traversing with ckmeta
     uint32_t gcksum;