diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs
index c88f5993889d..5f5d0c40fe3c 100644
--- a/src/librustc_codegen_llvm/back/lto.rs
+++ b/src/librustc_codegen_llvm/back/lto.rs
@@ -144,22 +144,15 @@ fn prepare_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
 /// for further optimization.
 pub(crate) fn run_fat(cgcx: &CodegenContext<LlvmCodegenBackend>,
                       modules: Vec<ModuleCodegen<ModuleLlvm>>,
-                      _cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
                       timeline: &mut Timeline)
-    -> Result<(Vec<LtoModuleCodegen<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError>
+    -> Result<LtoModuleCodegen<LlvmCodegenBackend>, FatalError>
 {
     let diag_handler = cgcx.create_diag_handler();
     let (symbol_white_list, upstream_modules) = prepare_lto(cgcx, timeline, &diag_handler)?;
     let symbol_white_list = symbol_white_list.iter()
                                              .map(|c| c.as_ptr())
                                              .collect::<Vec<_>>();
-    let opt_jobs = fat_lto(cgcx,
-                           &diag_handler,
-                           modules,
-                           upstream_modules,
-                           &symbol_white_list,
-                           timeline);
-    opt_jobs.map(|opt_jobs| (opt_jobs, vec![]))
+    fat_lto(cgcx, &diag_handler, modules, upstream_modules, &symbol_white_list, timeline)
 }
 
 /// Performs thin LTO by performing necessary global analysis and returning two
@@ -195,7 +188,7 @@ fn fat_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
            mut serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
            symbol_white_list: &[*const libc::c_char],
            timeline: &mut Timeline)
-    -> Result<Vec<LtoModuleCodegen<LlvmCodegenBackend>>, FatalError>
+    -> Result<LtoModuleCodegen<LlvmCodegenBackend>, FatalError>
 {
     info!("going for a fat lto");
 
@@ -284,10 +277,10 @@ fn fat_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
         timeline.record("passes");
     }
 
-    Ok(vec![LtoModuleCodegen::Fat {
+    Ok(LtoModuleCodegen::Fat {
         module: Some(module),
         _serialized_bitcode: serialized_bitcode,
-    }])
+    })
 }
 
 struct Linker<'a>(&'a mut llvm::Linker<'a>);
diff --git a/src/librustc_codegen_llvm/lib.rs b/src/librustc_codegen_llvm/lib.rs
index 7d941a99e2f2..4eb1fc1b1dc3 100644
--- a/src/librustc_codegen_llvm/lib.rs
+++ b/src/librustc_codegen_llvm/lib.rs
@@ -179,10 +179,9 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     fn run_fat_lto(
         cgcx: &CodegenContext<Self>,
         modules: Vec<ModuleCodegen<Self::Module>>,
-        cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
         timeline: &mut Timeline
-    ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError> {
-        back::lto::run_fat(cgcx, modules, cached_modules, timeline)
+    ) -> Result<LtoModuleCodegen<Self>, FatalError> {
+        back::lto::run_fat(cgcx, modules, timeline)
     }
     fn run_thin_lto(
         cgcx: &CodegenContext<Self>,
diff --git a/src/librustc_codegen_ssa/back/write.rs b/src/librustc_codegen_ssa/back/write.rs
index 5e89265d56f2..fe40cb184836 100644
--- a/src/librustc_codegen_ssa/back/write.rs
+++ b/src/librustc_codegen_ssa/back/write.rs
@@ -264,8 +264,10 @@ fn generate_lto_work<B: ExtraBackendMethods>(
 
     let (lto_modules, copy_jobs) = if !needs_fat_lto.is_empty() {
         assert!(needs_thin_lto.is_empty());
-        B::run_fat_lto(cgcx, needs_fat_lto, import_only_modules, &mut timeline)
-            .unwrap_or_else(|e| e.raise())
+        assert!(import_only_modules.is_empty());
+        let lto_module = B::run_fat_lto(cgcx, needs_fat_lto, &mut timeline)
+            .unwrap_or_else(|e| e.raise());
+        (vec![lto_module], vec![])
     } else {
         assert!(needs_fat_lto.is_empty());
         B::run_thin_lto(cgcx, needs_thin_lto, import_only_modules, &mut timeline)
diff --git a/src/librustc_codegen_ssa/traits/write.rs b/src/librustc_codegen_ssa/traits/write.rs
index 5bc44dfeeb32..7b8f9395f85e 100644
--- a/src/librustc_codegen_ssa/traits/write.rs
+++ b/src/librustc_codegen_ssa/traits/write.rs
@@ -29,9 +29,8 @@ pub trait WriteBackendMethods: 'static + Sized + Clone {
     fn run_fat_lto(
         cgcx: &CodegenContext<Self>,
         modules: Vec<ModuleCodegen<Self::Module>>,
-        cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
         timeline: &mut Timeline,
-    ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError>;
+    ) -> Result<LtoModuleCodegen<Self>, FatalError>;
     /// Performs thin LTO by performing necessary global analysis and returning two
     /// lists, one of the modules that need optimization and another for modules that
     /// can simply be copied over from the incr. comp. cache.