diff --git a/src/lib.rs b/src/lib.rs
index 4b7c211..c67e1b6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -53,8 +53,10 @@ fn serialize_fields(
 ) -> Vec<proc_macro2::TokenStream> {
     fields
         .iter()
-        .filter_map(|field| {
-            let index = field.index + offset;
+        .filter(|field| !field.skip_serializing_if.is_always())
+        .map(|field| {
+            // index should only be none if the field is always skipped, so this should never panic
+            let index = field.index.expect("index must be set for fields that are not skipped") + offset;
             let member = &field.member;
             let serialize_member = match &field.serialize_with {
                 None => quote!(&self.#member),
@@ -85,15 +87,15 @@ fn serialize_fields(
 
             // println!("field {:?} index {:?}", &field.label, field.index);
             match &field.skip_serializing_if {
-                Skip::If(path) => Some(quote! {
+                Skip::If(path) => quote! {
                     if !#path(&self.#member) {
                         map.serialize_entry(&#index, #serialize_member)?;
                     }
-                }),
-                Skip::Always => None,
-                Skip::Never => Some(quote! {
+                },
+                Skip::Always => unreachable!(),
+                Skip::Never => quote! {
                     map.serialize_entry(&#index, #serialize_member)?;
-                }),
+                },
             }
         })
         .collect()
@@ -222,7 +224,8 @@ fn match_fields(
         .map(|field| {
             let label = field.label.clone();
             let ident = format_ident!("{}", &field.label);
-            let index = field.index + offset;
+            // index should only be none if the field is always skipped, so this should never panic
+            let index = field.index.expect("index must be set for fields that are not skipped") + offset;
             let span = field.original_span;
 
             let next_value = match &field.deserialize_with {
diff --git a/src/parse.rs b/src/parse.rs
index 412aeef..651bbfe 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -36,7 +36,7 @@ impl Skip {
 pub struct Field {
     pub label: String,
     pub member: syn::Member,
-    pub index: usize,
+    pub index: Option<usize>,
     pub skip_serializing_if: Skip,
     pub serialize_with: Option<syn::ExprPath>,
     pub deserialize_with: Option<syn::ExprPath>,
@@ -221,15 +221,24 @@ fn parse_field(
         }
     }
 
-    let index = if attrs.auto_index {
-        auto_index
+    if explicit_index.is_some() && skip_serializing_if.is_always() {
+        return Err(Error::new_spanned(
+            field,
+            "`#[serde(index = ?]` and `#[serde(skip)]` cannot be combined",
+        ));
+    }
+
+    let index = if skip_serializing_if.is_always() {
+        None
+    } else if attrs.auto_index {
+        Some(auto_index)
     } else if let Some(index) = explicit_index {
         indices.push(index);
-        index
+        Some(index)
     } else {
         return Err(Error::new_spanned(
             field,
-            "Field without index attribute and `#[serde(auto_index)]` is not enabled on the struct",
+            "Field without index or skip attribute and `#[serde(auto_index)]` is not enabled on the struct",
         ));
     };
     Ok(Field {
diff --git a/tests/basics.rs b/tests/basics.rs
index eb1d149..9c0da1b 100644
--- a/tests/basics.rs
+++ b/tests/basics.rs
@@ -629,6 +629,8 @@ mod index {
         test2: usize,
         #[serde(index = 0x5A)]
         test3: usize,
+        #[serde(skip)]
+        test4: usize,
     }
 
     fn indices_example() -> WithIndices {
@@ -636,6 +638,7 @@ mod index {
             test1: 42,
             test2: 1,
             test3: 99,
+            test4: 0,
         }
     }