diff --git a/Makefile b/Makefile
index 268df6a6b4..8f38834193 100644
--- a/Makefile
+++ b/Makefile
@@ -4,6 +4,7 @@ SNAPSHOTS_IN=tests/in
 SNAPSHOTS_OUT=tests/out
 
 all:
+	cargo fmt
 	cargo test --all-features
 	cargo clippy --all-features
 
diff --git a/src/lib.rs b/src/lib.rs
index 6f491d6f47..1921b4d7ae 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -471,6 +471,8 @@ pub struct GlobalVariable {
     pub ty: Handle<Type>,
     /// Initial value for this variable.
     pub init: Option<Handle<Constant>>,
+    //TODO: require fragment input interpolation once the entry point I/O
+    // is refactored.
     /// The interpolation qualifier, if any.
     /// If the this `GlobalVariable` is a vertex output
     /// or fragment input, `None` corresponds to the
diff --git a/src/proc/validator.rs b/src/proc/validator.rs
index 92306d9598..1bc45087f9 100644
--- a/src/proc/validator.rs
+++ b/src/proc/validator.rs
@@ -249,8 +249,8 @@ pub enum EntryPointError {
     BindingCollision(Handle<crate::GlobalVariable>),
     #[error("Built-in {0:?} is not applicable to this entry point")]
     InvalidBuiltIn(crate::BuiltIn),
-    #[error("Interpolation of an integer has to be flat")]
-    InvalidIntegerInterpolation,
+    #[error("Location {location} onterpolation of an integer has to be flat")]
+    InvalidIntegerInterpolation { location: u32 },
     #[error(transparent)]
     Function(#[from] FunctionError),
 }
@@ -1091,19 +1091,16 @@ impl Validator {
                 continue;
             }
 
-            if let Some(crate::Binding::Location(_)) = var.binding {
-                match (stage, var.class) {
-                    (crate::ShaderStage::Vertex, crate::StorageClass::Output)
-                    | (crate::ShaderStage::Fragment, crate::StorageClass::Input) => {
-                        match module.types[var.ty].inner.scalar_kind() {
-                            Some(crate::ScalarKind::Float) => {}
-                            Some(_) if var.interpolation != Some(crate::Interpolation::Flat) => {
-                                return Err(EntryPointError::InvalidIntegerInterpolation);
-                            }
-                            _ => {}
+            if let Some(crate::Binding::Location(location)) = var.binding {
+                if stage == crate::ShaderStage::Fragment && var.class == crate::StorageClass::Input
+                {
+                    match module.types[var.ty].inner.scalar_kind() {
+                        Some(crate::ScalarKind::Float) => {}
+                        Some(_) if var.interpolation != Some(crate::Interpolation::Flat) => {
+                            return Err(EntryPointError::InvalidIntegerInterpolation { location });
                         }
+                        _ => {}
                     }
-                    _ => {}
                 }
             }