diff --git a/src/models.rs b/src/models.rs
index 478130d..2bfd46c 100644
--- a/src/models.rs
+++ b/src/models.rs
@@ -3,7 +3,7 @@ use strum_macros::Display;
 use url::Url;
 use validator::{Validate, ValidationError};
 
-#[derive(Debug, Deserialize, Display, PartialEq)]
+#[derive(Clone, Copy, Debug, Deserialize, Display, PartialEq)]
 #[serde(rename_all = "lowercase")]
 pub enum DType {
     Int32,
@@ -14,6 +14,20 @@ pub enum DType {
     Float64,
 }
 
+impl DType {
+    /// Returns the size of the associated type in bytes.
+    fn size_of(self) -> usize {
+        match self {
+            Self::Int32 => std::mem::size_of::<i32>(),
+            Self::Int64 => std::mem::size_of::<i64>(),
+            Self::Uint32 => std::mem::size_of::<u32>(),
+            Self::Uint64 => std::mem::size_of::<u64>(),
+            Self::Float32 => std::mem::size_of::<f32>(),
+            Self::Float64 => std::mem::size_of::<f64>(),
+        }
+    }
+}
+
 #[derive(Debug, Deserialize, PartialEq)]
 pub enum Order {
     C,
@@ -67,15 +81,28 @@ fn validate_request_data(request_data: &RequestData) -> Result<(), ValidationErr
     // Validation of multiple fields in RequestData.
     // TODO: More validation of shape & selection vs. size
     // TODO: More validation that selection fits in shape
-    if let Some(shape) = &request_data.shape {
-        if let Some(selection) = &request_data.selection {
+    if let Some(size) = &request_data.size {
+        if (*size as usize) % request_data.dtype.size_of() != 0 {
+            return Err(ValidationError::new(
+                "Size must be a multiple of dtype size in bytes",
+            ));
+        }
+    };
+    match (&request_data.shape, &request_data.selection) {
+        (Some(shape), Some(selection)) => {
             if shape.len() != selection.len() {
                 return Err(ValidationError::new(
                     "Shape and selection must have the same length",
                 ));
             }
         }
-    }
+        (None, Some(_)) => {
+            return Err(ValidationError::new(
+                "Selection requires shape to be specified",
+            ));
+        }
+        _ => (),
+    };
     Ok(())
 }
 
@@ -121,8 +148,8 @@ mod tests {
             bucket: "bar".to_string(),
             object: "baz".to_string(),
             dtype: DType::Int32,
-            offset: Some(1),
-            size: Some(2),
+            offset: Some(4),
+            size: Some(8),
             shape: Some(vec![1, 2]),
             order: Some(Order::C),
             selection: Some(vec![
@@ -191,10 +218,10 @@ mod tests {
                 Token::Unit,
                 Token::Str("offset"),
                 Token::Some,
-                Token::U32(1),
+                Token::U32(4),
                 Token::Str("size"),
                 Token::Some,
-                Token::U32(2),
+                Token::U32(8),
                 Token::Str("shape"),
                 Token::Some,
                 Token::Seq { len: Some(2) },
@@ -405,6 +432,14 @@ mod tests {
         request_data.validate().unwrap()
     }
 
+    #[test]
+    #[should_panic(expected = "Size must be a multiple of dtype size in bytes")]
+    fn test_invalid_size_for_dtype() {
+        let mut request_data = get_test_request_data();
+        request_data.size = Some(1);
+        request_data.validate().unwrap()
+    }
+
     #[test]
     #[should_panic(expected = "Shape and selection must have the same length")]
     fn test_shape_selection_mismatch() {
@@ -418,6 +453,17 @@ mod tests {
         request_data.validate().unwrap()
     }
 
+    #[test]
+    #[should_panic(expected = "Selection requires shape to be specified")]
+    fn test_selection_without_shape() {
+        let mut request_data = get_test_request_data();
+        request_data.selection = Some(vec![Slice {
+            start: 1,
+            end: 2,
+            stride: 1,
+        }]);
+        request_data.validate().unwrap()
+    }
     #[test]
     fn test_unknown_field() {
         assert_de_tokens_error::<RequestData>(&[
@@ -440,7 +486,7 @@ mod tests {
 
     #[test]
     fn test_json_optional_fields() {
-        let json = r#"{"source": "http://example.com", "bucket": "bar", "object": "baz", "dtype": "int32", "offset": 1, "size": 2, "shape": [1, 2], "order": "C", "selection": [[1, 2, 3], [4, 5, 6]]}"#;
+        let json = r#"{"source": "http://example.com", "bucket": "bar", "object": "baz", "dtype": "int32", "offset": 4, "size": 8, "shape": [1, 2], "order": "C", "selection": [[1, 2, 3], [4, 5, 6]]}"#;
         let request_data = serde_json::from_str::<RequestData>(json).unwrap();
         assert_eq!(request_data, get_test_request_data_optional());
     }