diff --git a/lib/api/src/conversions/vectors.rs b/lib/api/src/conversions/vectors.rs
index 1c6720bbe3..4e18a3189e 100644
--- a/lib/api/src/conversions/vectors.rs
+++ b/lib/api/src/conversions/vectors.rs
@@ -15,6 +15,12 @@ fn convert_to_plain_multi_vector(
     data: Vec<f32>,
     vectors_count: usize,
 ) -> Result<MultiDenseVector, OperationError> {
+    if vectors_count == 0 || data.is_empty() {
+        return Err(OperationError::validation_error(format!(
+            "Empty multi-vector data with vectors count: {vectors_count}"
+        )));
+    }
+
     let dim = data.len() / vectors_count;
     if dim * vectors_count != data.len() {
         return Err(OperationError::validation_error(format!(
diff --git a/lib/common/common/src/validation.rs b/lib/common/common/src/validation.rs
index 0bb372a8fc..740bf03552 100644
--- a/lib/common/common/src/validation.rs
+++ b/lib/common/common/src/validation.rs
@@ -302,6 +302,14 @@ pub fn validate_multi_vector_len(
         return Err(errors);
     }
 
+    if flatten_dense_vector.is_empty() {
+        let mut errors = ValidationErrors::default();
+        let mut err = ValidationError::new("empty_multi_vector");
+        err.add_param(Cow::from("message"), &"multi vector must not be empty");
+        errors.add("data", err);
+        return Err(errors);
+    }
+
     let dense_vector_len = flatten_dense_vector.len();
     if dense_vector_len >= MAX_MULTIVECTOR_FLATTENED_LEN {
         let mut errors = ValidationErrors::default();
@@ -328,6 +336,17 @@ pub fn validate_multi_vector_len(
 mod tests {
     use super::*;
 
+    #[test]
+    fn test_validate_multi_vector_len_rejects_empty_data() {
+        // Regression: empty flattened data with a positive vectors_count must be
+        // rejected. Previously this returned Ok (0.is_multiple_of(N) == true), and
+        // the value then reached convert_to_plain_multi_vector, which builds
+        // chunks(dim) with dim == 0 and panics on the gRPC upsert path.
+        assert!(validate_multi_vector_len(2, &[]).is_err());
+        // A non-empty, consistent multivector still validates.
+        assert!(validate_multi_vector_len(2, &[1.0, 2.0, 3.0, 4.0]).is_ok());
+    }
+
     #[test]
     fn test_validate_range_generic() {
         assert!(validate_range_generic(u64::MIN, None, None).is_ok());