diff --git a/internal/wire/parse.go b/internal/wire/parse.go
index a1d939d..1b65312 100644
--- a/internal/wire/parse.go
+++ b/internal/wire/parse.go
@@ -193,7 +193,11 @@ func Load(bctx *build.Context, wd string, pkgs []string) (*Info, []error) {
 				if !ok {
 					continue
 				}
-				buildCall := isInjector(&pkgInfo.Info, fn)
+				buildCall, err := findInjectorBuild(&pkgInfo.Info, fn)
+				if err != nil {
+					ec.add(notePosition(prog.Fset.Position(fn.Pos()), fmt.Errorf("inject %s: %v", fn.Name.Name, err)))
+					continue
+				}
 				if buildCall == nil {
 					continue
 				}
@@ -770,53 +774,59 @@ func processInterfaceValue(fset *token.FileSet, info *types.Info, call *ast.Call
 	}, nil
 }
 
-// isInjector checks whether a given function declaration is an
-// injector template, returning the wire.Build call. It returns nil if
-// the function is not an injector template.
-func isInjector(info *types.Info, fn *ast.FuncDecl) *ast.CallExpr {
+// findInjectorBuild returns the wire.Build call if fn is an injector template.
+// It returns nil if the function is not an injector template.
+func findInjectorBuild(info *types.Info, fn *ast.FuncDecl) (*ast.CallExpr, error) {
 	if fn.Body == nil {
-		return nil
+		return nil, nil
 	}
-	var only *ast.ExprStmt
+	numStatements := 0
+	invalid := false
+	var wireBuildCall *ast.CallExpr
 	for _, stmt := range fn.Body.List {
 		switch stmt := stmt.(type) {
 		case *ast.ExprStmt:
-			if only != nil {
-				return nil
+			numStatements++
+			if numStatements > 1 {
+				invalid = true
 			}
-			only = stmt
+			call, ok := stmt.X.(*ast.CallExpr)
+			if !ok {
+				continue
+			}
+			if qualifiedIdentObject(info, call.Fun) == types.Universe.Lookup("panic") {
+				if len(call.Args) != 1 {
+					continue
+				}
+				call, ok = call.Args[0].(*ast.CallExpr)
+				if !ok {
+					continue
+				}
+			}
+			buildObj := qualifiedIdentObject(info, call.Fun)
+			if buildObj == nil || buildObj.Pkg() == nil || !isWireImport(buildObj.Pkg().Path()) || buildObj.Name() != "Build" {
+				continue
+			}
+			wireBuildCall = call
 		case *ast.EmptyStmt:
 			// Do nothing.
 		case *ast.ReturnStmt:
 			// Allow the function to end in a return.
-			if only == nil {
-				return nil
+			if numStatements == 0 {
+				return nil, nil
 			}
 		default:
-			return nil
+			invalid = true
 		}
+
 	}
-	if only == nil {
-		return nil
+	if wireBuildCall == nil {
+		return nil, nil
 	}
-	call, ok := only.X.(*ast.CallExpr)
-	if !ok {
-		return nil
+	if invalid {
+		return nil, errors.New("a call to wire.Build indicates that this function is an injector, but injectors must consist of only the wire.Build call and an optional return")
 	}
-	if qualifiedIdentObject(info, call.Fun) == types.Universe.Lookup("panic") {
-		if len(call.Args) != 1 {
-			return nil
-		}
-		call, ok = call.Args[0].(*ast.CallExpr)
-		if !ok {
-			return nil
-		}
-	}
-	buildObj := qualifiedIdentObject(info, call.Fun)
-	if buildObj == nil || buildObj.Pkg() == nil || !isWireImport(buildObj.Pkg().Path()) || buildObj.Name() != "Build" {
-		return nil
-	}
-	return call
+	return wireBuildCall, nil
 }
 
 func isWireImport(path string) bool {
diff --git a/internal/wire/testdata/InvalidInjector/foo/foo.go b/internal/wire/testdata/InvalidInjector/foo/foo.go
new file mode 100644
index 0000000..922b980
--- /dev/null
+++ b/internal/wire/testdata/InvalidInjector/foo/foo.go
@@ -0,0 +1,36 @@
+// Copyright 2018 The Go Cloud Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	foo := injectFoo()
+	bar := injectBar()
+	fmt.Println(foo)
+	fmt.Println(bar)
+}
+
+type Foo int
+type Bar int
+
+func provideFoo() Foo {
+	return Foo(42)
+}
+func provideBar() Bar {
+	return Bar(99)
+}
diff --git a/internal/wire/testdata/InvalidInjector/foo/wire.go b/internal/wire/testdata/InvalidInjector/foo/wire.go
new file mode 100644
index 0000000..128e88c
--- /dev/null
+++ b/internal/wire/testdata/InvalidInjector/foo/wire.go
@@ -0,0 +1,33 @@
+// Copyright 2018 The Go Cloud Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//+build wireinject
+
+package main
+
+import (
+	"github.com/google/go-cloud/wire"
+)
+
+func injectFoo() Foo {
+	// This non-call statement makes this an invalid injector.
+	 _ = 42
+	panic(wire.Build(provideFoo))
+}
+
+func injectBar() Bar {
+	// Two call statements are also invalid.
+	panic(wire.Build(provideBar))
+	panic(wire.Build(provideBar))
+}
diff --git a/internal/wire/testdata/InvalidInjector/pkg b/internal/wire/testdata/InvalidInjector/pkg
new file mode 100644
index 0000000..f7a5c8c
--- /dev/null
+++ b/internal/wire/testdata/InvalidInjector/pkg
@@ -0,0 +1 @@
+example.com/foo
diff --git a/internal/wire/testdata/InvalidInjector/want/wire_errs.txt b/internal/wire/testdata/InvalidInjector/want/wire_errs.txt
new file mode 100644
index 0000000..fbd6607
--- /dev/null
+++ b/internal/wire/testdata/InvalidInjector/want/wire_errs.txt
@@ -0,0 +1,4 @@
+a call to wire.Build indicates that this function is an injector, but injectors
+must consist of only the wire.Build call and an optional return
+a call to wire.Build indicates that this function is an injector, but injectors
+must consist of only the wire.Build call and an optional return
diff --git a/internal/wire/wire.go b/internal/wire/wire.go
index f064aac..ef748cb 100644
--- a/internal/wire/wire.go
+++ b/internal/wire/wire.go
@@ -75,7 +75,11 @@ func generateInjectors(g *gen, pkgInfo *loader.PackageInfo) (injectorFiles []*as
 			if !ok {
 				continue
 			}
-			buildCall := isInjector(&pkgInfo.Info, fn)
+			buildCall, err := findInjectorBuild(&pkgInfo.Info, fn)
+			if err != nil {
+				ec.add(err)
+				continue
+			}
 			if buildCall == nil {
 				continue
 			}
@@ -113,7 +117,9 @@ func copyNonInjectorDecls(g *gen, files []*ast.File, info *types.Info) {
 		for _, decl := range f.Decls {
 			switch decl := decl.(type) {
 			case *ast.FuncDecl:
-				if isInjector(info, decl) != nil {
+				// OK to ignore error, as any error cases should already have
+				// been filtered out.
+				if buildCall, _ := findInjectorBuild(info, decl); buildCall != nil {
 					continue
 				}
 			case *ast.GenDecl: