diff --git a/src/go/types/api.go b/src/go/types/api.go
index 2dd5a3e3c0..4583b4f7b5 100644
--- a/src/go/types/api.go
+++ b/src/go/types/api.go
@@ -286,10 +286,10 @@ type Info struct {
 	// appear in this list.
 	InitOrder []*Initializer
 
-	// _FileVersions maps a file to the file's Go version.
+	// _FileVersions maps a file's start position to the file's Go version.
 	// If the file doesn't specify a version and Config.GoVersion is not
 	// given, the reported version is the zero version (Major, Minor = 0, 0).
-	_FileVersions map[*token.File]_Version
+	_FileVersions map[token.Pos]_Version
 }
 
 func (info *Info) recordTypes() bool {
diff --git a/src/go/types/check.go b/src/go/types/check.go
index f3ad85dff9..6aaab064c5 100644
--- a/src/go/types/check.go
+++ b/src/go/types/check.go
@@ -99,12 +99,12 @@ type Checker struct {
 	fset *token.FileSet
 	pkg  *Package
 	*Info
-	version version                 // accepted language version
-	posVers map[*token.File]version // maps files to versions (may be nil)
-	nextID  uint64                  // unique Id for type parameters (first valid Id is 1)
-	objMap  map[Object]*declInfo    // maps package-level objects and (non-interface) methods to declaration info
-	impMap  map[importKey]*Package  // maps (import path, source directory) to (complete or fake) package
-	valids  instanceLookup          // valid *Named (incl. instantiated) types per the validType check
+	version version                // accepted language version
+	posVers map[token.Pos]version  // maps file start positions to versions (may be nil)
+	nextID  uint64                 // unique Id for type parameters (first valid Id is 1)
+	objMap  map[Object]*declInfo   // maps package-level objects and (non-interface) methods to declaration info
+	impMap  map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
+	valids  instanceLookup         // valid *Named (incl. instantiated) types per the validType check
 
 	// pkgPathMap maps package names to the set of distinct import paths we've
 	// seen for that name, anywhere in the import graph. It is used for
@@ -288,8 +288,8 @@ func (check *Checker) initFiles(files []*ast.File) {
 	}
 
 	for _, file := range check.files {
-		tfile := check.fset.File(file.FileStart)
-		check.recordFileVersion(tfile, check.version) // record package version (possibly zero version)
+		fbase := file.FileStart
+		check.recordFileVersion(fbase, check.version) // record package version (possibly zero version)
 		v, _ := parseGoVersion(file.GoVersion)
 		if v.major > 0 {
 			if v.equal(check.version) {
@@ -312,10 +312,10 @@ func (check *Checker) initFiles(files []*ast.File) {
 				continue
 			}
 			if check.posVers == nil {
-				check.posVers = make(map[*token.File]version)
+				check.posVers = make(map[token.Pos]version)
 			}
-			check.posVers[tfile] = v
-			check.recordFileVersion(tfile, v) // overwrite package version
+			check.posVers[fbase] = v
+			check.recordFileVersion(fbase, v) // overwrite package version
 		}
 	}
 }
@@ -640,8 +640,8 @@ func (check *Checker) recordScope(node ast.Node, scope *Scope) {
 	}
 }
 
-func (check *Checker) recordFileVersion(tfile *token.File, v version) {
+func (check *Checker) recordFileVersion(pos token.Pos, v version) {
 	if m := check._FileVersions; m != nil {
-		m[tfile] = _Version{v.major, v.minor}
+		m[pos] = _Version{v.major, v.minor}
 	}
 }
diff --git a/src/go/types/version.go b/src/go/types/version.go
index 108d9b34a0..2f21e98ad8 100644
--- a/src/go/types/version.go
+++ b/src/go/types/version.go
@@ -133,7 +133,8 @@ func (check *Checker) allowVersion(pkg *Package, at positioner, v version) bool
 
 	// If the source file declares its Go version, use that to decide.
 	if check.posVers != nil {
-		if src, ok := check.posVers[check.fset.File(at.Pos())]; ok && src.major >= 1 {
+		fileStart := check.fset.File(at.Pos()).Pos(0)
+		if src, ok := check.posVers[fileStart]; ok && src.major >= 1 {
 			return !src.before(v)
 		}
 	}