diff --git a/rust/lancedb/src/index/vector.rs b/rust/lancedb/src/index/vector.rs
index f287ce2f..ddbbc7e8 100644
--- a/rust/lancedb/src/index/vector.rs
+++ b/rust/lancedb/src/index/vector.rs
@@ -214,6 +214,11 @@ pub(crate) fn suggested_num_partitions(rows: usize) -> u32 {
     max(1, num_partitions)
 }
 
+pub(crate) fn suggested_num_partitions_for_hnsw(rows: usize, dim: u32) -> u32 {
+    let num_partitions = (((rows as u64) * (dim as u64)) / (256 * 5_000_000)) as u32;
+    max(1, num_partitions)
+}
+
 pub(crate) fn suggested_num_sub_vectors(dim: u32) -> u32 {
     if dim % 16 == 0 {
         // Should be more aggressive than this default.
diff --git a/rust/lancedb/src/table.rs b/rust/lancedb/src/table.rs
index 86fd1d1b..109ebcd4 100644
--- a/rust/lancedb/src/table.rs
+++ b/rust/lancedb/src/table.rs
@@ -54,7 +54,8 @@ use crate::embeddings::{EmbeddingDefinition, EmbeddingRegistry, MaybeEmbedded, M
 use crate::error::{Error, Result};
 use crate::index::scalar::FtsIndexBuilder;
 use crate::index::vector::{
-    IvfHnswPqIndexBuilder, IvfHnswSqIndexBuilder, IvfPqIndexBuilder, VectorIndex,
+    suggested_num_partitions_for_hnsw, IvfHnswPqIndexBuilder, IvfHnswSqIndexBuilder,
+    IvfPqIndexBuilder, VectorIndex,
 };
 use crate::index::IndexConfig;
 use crate::index::IndexStatistics;
@@ -1440,11 +1441,19 @@ impl NativeTable {
             });
         }
 
-        let num_partitions = if let Some(n) = index.num_partitions {
+        let num_partitions: u32 = if let Some(n) = index.num_partitions {
             n
         } else {
-            suggested_num_partitions(self.count_rows(None).await?)
+            match field.data_type() {
+                arrow_schema::DataType::FixedSizeList(_, n) => Ok::<u32, Error>(
+                    suggested_num_partitions_for_hnsw(self.count_rows(None).await?, *n as u32),
+                ),
+                _ => Err(Error::Schema {
+                    message: format!("Column '{}' is not a FixedSizeList", field.name()),
+                }),
+            }?
         };
+
         let num_sub_vectors: u32 = if let Some(n) = index.num_sub_vectors {
             n
         } else {
@@ -1503,10 +1512,17 @@ impl NativeTable {
             });
         }
 
-        let num_partitions = if let Some(n) = index.num_partitions {
+        let num_partitions: u32 = if let Some(n) = index.num_partitions {
             n
         } else {
-            suggested_num_partitions(self.count_rows(None).await?)
+            match field.data_type() {
+                arrow_schema::DataType::FixedSizeList(_, n) => Ok::<u32, Error>(
+                    suggested_num_partitions_for_hnsw(self.count_rows(None).await?, *n as u32),
+                ),
+                _ => Err(Error::Schema {
+                    message: format!("Column '{}' is not a FixedSizeList", field.name()),
+                }),
+            }?
         };
 
         let mut dataset = self.dataset.get_mut().await?;