diff --git a/crates/byondapi-rs/src/map.rs b/crates/byondapi-rs/src/map.rs
index d46fdfe..e559192 100644
--- a/crates/byondapi-rs/src/map.rs
+++ b/crates/byondapi-rs/src/map.rs
@@ -38,6 +38,7 @@ pub fn byond_block(corner1: ByondXYZ, corner2: ByondXYZ) -> Result<Vec<ByondValu
     }
 
     BUFFER.with_borrow_mut(|buff| -> Result<Vec<ByondValue>, Error> {
+        let initial_len = buff.capacity() as u32;
         let mut len = buff.capacity() as u32;
         // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
         let initial_res = unsafe {
@@ -45,7 +46,8 @@ pub fn byond_block(corner1: ByondXYZ, corner2: ByondXYZ) -> Result<Vec<ByondValu
         };
         match (initial_res, len) {
             (false, 1..) => {
-                buff.reserve_exact(len as usize);
+                debug_assert!(len > initial_len);
+                buff.reserve_exact((len - initial_len) as usize);
                 // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
                 unsafe {
                     map_byond_error!(byond().Byond_Block(
diff --git a/crates/byondapi-rs/src/value/functions.rs b/crates/byondapi-rs/src/value/functions.rs
index 05ee416..4ce9eb1 100644
--- a/crates/byondapi-rs/src/value/functions.rs
+++ b/crates/byondapi-rs/src/value/functions.rs
@@ -42,13 +42,15 @@ impl ByondValue {
         }
 
         let bytes = BUFFER.with_borrow_mut(|buff| -> Result<Vec<u8>, Error> {
+            let initial_len = buff.capacity() as u32;
             let mut len = buff.capacity() as u32;
             // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
             let initial_res =
                 unsafe { byond().Byond_ToString(&self.0, buff.as_mut_ptr().cast(), &mut len) };
             match (initial_res, len) {
                 (false, 1..) => {
-                    buff.reserve_exact(len as usize);
+                    debug_assert!(len > initial_len);
+                    buff.reserve_exact((len - initial_len) as usize);
                     // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
                     unsafe {
                         map_byond_error!(byond().Byond_ToString(
diff --git a/crates/byondapi-rs/src/value/list.rs b/crates/byondapi-rs/src/value/list.rs
index a93d3bf..8435e83 100644
--- a/crates/byondapi-rs/src/value/list.rs
+++ b/crates/byondapi-rs/src/value/list.rs
@@ -13,6 +13,7 @@ impl ByondValue {
         }
 
         BUFFER.with_borrow_mut(|buff| -> Result<Vec<ByondValue>, Error> {
+            let initial_len = buff.capacity() as u32;
             let mut len = buff.capacity() as u32;
 
             // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
@@ -20,7 +21,8 @@ impl ByondValue {
                 unsafe { byond().Byond_ReadList(&self.0, buff.as_mut_ptr().cast(), &mut len) };
             match (initial_res, len) {
                 (false, 1..) => {
-                    buff.reserve_exact(len as usize);
+                    debug_assert!(len > initial_len);
+                    buff.reserve_exact((len - initial_len) as usize);
                     // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
                     unsafe {
                         map_byond_error!(byond().Byond_ReadList(
@@ -56,6 +58,7 @@ impl ByondValue {
         }
 
         BUFFER.with_borrow_mut(|buff| -> Result<Vec<ByondValue>, Error> {
+            let initial_len = buff.capacity() as u32;
             let mut len = buff.capacity() as u32;
 
             // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
@@ -63,7 +66,8 @@ impl ByondValue {
                 unsafe { byond().Byond_ReadListAssoc(&self.0, buff.as_mut_ptr().cast(), &mut len) };
             match (initial_res, len) {
                 (false, 1..) => {
-                    buff.reserve_exact(len as usize);
+                    debug_assert!(len > initial_len);
+                    buff.reserve_exact((len - initial_len) as usize);
                     // Safety: buffer capacity is passed to byond, which makes sure it writes in-bound
                     unsafe {
                         map_byond_error!(byond().Byond_ReadListAssoc(