diff --git a/src/analyze/basic_block.rs b/src/analyze/basic_block.rs
index 97ae3ec0..35ab10d5 100644
--- a/src/analyze/basic_block.rs
+++ b/src/analyze/basic_block.rs
@@ -920,12 +920,25 @@ impl<'tcx, 'ctx> Analyzer<'tcx, 'ctx> {
         }
     }
 
+    /// Analyzes the body of the implementation a call dispatches to.
+    ///
+    /// A call typed by a trait method's spec never asks for the implementing method's type, and
+    /// an implementation with generic parameters is analyzed only when its type is asked for.
+    fn analyze_resolved_impl_body(&mut self, def_id: DefId, args: mir_ty::GenericArgsRef<'tcx>) {
+        let (impl_def_id, impl_args) = self.resolve_fn_def(def_id, args);
+        if impl_def_id == def_id {
+            return;
+        }
+        let _ = self.ctx.def_ty_with_args(impl_def_id, impl_args);
+    }
+
     fn fn_def_ty(
         &mut self,
         def_id: DefId,
         args: mir_ty::GenericArgsRef<'tcx>,
     ) -> rty::Type<rty::Closed> {
         if let Some(def_ty) = self.ctx.def_ty_with_args(def_id, args) {
+            self.analyze_resolved_impl_body(def_id, args);
             return def_ty.ty;
         }
 
diff --git a/src/analyze/local_def.rs b/src/analyze/local_def.rs
index a98eb1ce..f4b51a6e 100644
--- a/src/analyze/local_def.rs
+++ b/src/analyze/local_def.rs
@@ -45,6 +45,7 @@ pub struct Analyzer<'tcx, 'ctx> {
     local_def_id: LocalDefId,
 
     body: Body<'tcx>,
+    /// the instantiation of the def's generic parameters being analyzed, also used
     /// to substitute HIR types during translation in [`crate::analyze::annot_fn`]
     generic_args: mir_ty::GenericArgsRef<'tcx>,
     drop_points: HashMap<BasicBlock, analyze::basic_block::DropPoints>,
@@ -198,7 +199,11 @@ impl<'tcx, 'ctx> Analyzer<'tcx, 'ctx> {
             return None;
         }
 
-        let trait_ref = self.tcx.impl_trait_ref(impl_did)?.instantiate_identity();
+        // an associated method's generic arguments start with those of its impl
+        let trait_ref = self
+            .tcx
+            .impl_trait_ref(impl_did)?
+            .instantiate(self.tcx, self.generic_args);
         let trait_item_did = self
             .tcx
             .associated_item(self.local_def_id.to_def_id())
@@ -1115,7 +1120,7 @@ impl<'tcx, 'ctx> Analyzer<'tcx, 'ctx> {
         let body = tcx.optimized_mir(local_def_id.to_def_id()).clone();
         let drop_points = Default::default();
         let type_builder = TypeBuilder::new(tcx, ctx.def_ids(), local_def_id.to_def_id());
-        let generic_args = tcx.mk_args(&[]);
+        let generic_args = mir_ty::GenericArgs::identity_for_item(tcx, local_def_id);
         Self {
             ctx,
             tcx,
diff --git a/tests/ui/fail/trait_generic_impl.rs b/tests/ui/fail/trait_generic_impl.rs
new file mode 100644
index 00000000..0f9430a8
--- /dev/null
+++ b/tests/ui/fail/trait_generic_impl.rs
@@ -0,0 +1,29 @@
+//@error-in-other-file: Unsat
+//@compile-flags: -C debug-assertions=off
+
+#[thrust_macros::context]
+trait Tr {
+    #[thrust_macros::requires(true)]
+    #[thrust_macros::ensures(result > 0)]
+    fn m(&self) -> i32;
+}
+
+struct W<T>(T);
+
+impl<T> thrust_models::Model for W<T>
+where
+    T: thrust_models::Model,
+{
+    type Ty = Self;
+}
+
+impl<T> Tr for W<T> {
+    fn m(&self) -> i32 {
+        -1
+    }
+}
+
+fn main() {
+    let w = W(0i32);
+    assert!(w.m() > 0);
+}
diff --git a/tests/ui/pass/trait_generic_impl.rs b/tests/ui/pass/trait_generic_impl.rs
new file mode 100644
index 00000000..b8a4abee
--- /dev/null
+++ b/tests/ui/pass/trait_generic_impl.rs
@@ -0,0 +1,29 @@
+//@check-pass
+//@compile-flags: -C debug-assertions=off
+
+#[thrust_macros::context]
+trait Tr {
+    #[thrust_macros::requires(true)]
+    #[thrust_macros::ensures(result > 0)]
+    fn m(&self) -> i32;
+}
+
+struct W<T>(T);
+
+impl<T> thrust_models::Model for W<T>
+where
+    T: thrust_models::Model,
+{
+    type Ty = Self;
+}
+
+impl<T> Tr for W<T> {
+    fn m(&self) -> i32 {
+        1
+    }
+}
+
+fn main() {
+    let w = W(0i32);
+    assert!(w.m() > 0);
+}