diff --git a/build/build.go b/build/build.go
index 399f3b5e0..84e486a7f 100644
--- a/build/build.go
+++ b/build/build.go
@@ -55,7 +55,8 @@ func Import(path string, mode build.ImportMode, archSuffix string) (*build.Packa
 	}
 	if _, err := os.Stat(pkg.PkgObj); os.IsNotExist(err) && strings.HasPrefix(pkg.PkgObj, build.Default.GOROOT) {
 		// fall back to GOPATH
-		gopathPkgObj := build.Default.GOPATH + pkg.PkgObj[len(build.Default.GOROOT):]
+		firstGopathWorkspace := filepath.SplitList(build.Default.GOPATH)[0] // TODO: Need to check inside all GOPATH workspaces.
+		gopathPkgObj := filepath.Join(firstGopathWorkspace, pkg.PkgObj[len(build.Default.GOROOT):])
 		if _, err := os.Stat(gopathPkgObj); err == nil {
 			pkg.PkgObj = gopathPkgObj
 		}
@@ -361,8 +362,9 @@ func (s *Session) BuildPackage(pkg *PackageData) error {
 
 	if err := s.writeLibraryPackage(pkg, pkg.PkgObj); err != nil {
 		if strings.HasPrefix(pkg.PkgObj, s.options.GOROOT) {
-			// fall back to GOPATH
-			if err := s.writeLibraryPackage(pkg, s.options.GOPATH+pkg.PkgObj[len(s.options.GOROOT):]); err != nil {
+			// fall back to first GOPATH workspace
+			firstGopathWorkspace := filepath.SplitList(s.options.GOPATH)[0]
+			if err := s.writeLibraryPackage(pkg, filepath.Join(firstGopathWorkspace, pkg.PkgObj[len(s.options.GOROOT):])); err != nil {
 				return err
 			}
 			return nil
@@ -421,9 +423,9 @@ func (s *Session) WriteCommandPackage(pkg *PackageData, pkgObj string) error {
 			}
 			pos := fileSet.Position(originalPos)
 			file := pos.Filename
-			switch {
-			case strings.HasPrefix(file, s.options.GOPATH):
-				file = filepath.ToSlash(filepath.Join("/gopath", file[len(s.options.GOPATH):]))
+			switch hasGopathPrefix, prefixLen := hasGopathPrefix(file, s.options.GOPATH); {
+			case hasGopathPrefix:
+				file = filepath.ToSlash(filepath.Join("/gopath", file[prefixLen:]))
 			case strings.HasPrefix(file, s.options.GOROOT):
 				file = filepath.ToSlash(filepath.Join("/goroot", file[len(s.options.GOROOT):]))
 			default:
@@ -440,6 +442,18 @@ func (s *Session) WriteCommandPackage(pkg *PackageData, pkgObj string) error {
 	return compiler.WriteProgramCode(deps, s.ImportContext, sourceMapFilter)
 }
 
+// hasGopathPrefix returns true and the length of the matched GOPATH workspace,
+// iff file has a prefix that matches one of the GOPATH workspaces.
+func hasGopathPrefix(file, gopath string) (hasGopathPrefix bool, prefixLen int) {
+	gopathWorkspaces := filepath.SplitList(gopath)
+	for _, gopathWorkspace := range gopathWorkspaces {
+		if strings.HasPrefix(file, gopathWorkspace) {
+			return true, len(gopathWorkspace)
+		}
+	}
+	return false, 0
+}
+
 func (s *Session) WaitForChange() {
 	fmt.Println("\x1B[32mwatching for changes...\x1B[39m")
 	select {
diff --git a/tool.go b/tool.go
index cd58ec856..e166564f3 100644
--- a/tool.go
+++ b/tool.go
@@ -136,7 +136,8 @@ func main() {
 			exitCode := handleError(func() error {
 				pkgs := installFlags.Args()
 				if len(pkgs) == 0 {
-					srcDir, err := filepath.EvalSymlinks(filepath.Join(build.Default.GOPATH, "src"))
+					firstGopathWorkspace := filepath.SplitList(build.Default.GOPATH)[0] // TODO: The GOPATH workspace that contains the package source should be chosen.
+					srcDir, err := filepath.EvalSymlinks(filepath.Join(firstGopathWorkspace, "src"))
 					if err != nil {
 						return err
 					}
@@ -220,7 +221,8 @@ func main() {
 				}
 			}
 			if len(pkgs) == 0 {
-				srcDir, err := filepath.EvalSymlinks(filepath.Join(build.Default.GOPATH, "src"))
+				firstGopathWorkspace := filepath.SplitList(build.Default.GOPATH)[0] // TODO: Not sure if always picking first GOPATH workspace here is the right thing.
+				srcDir, err := filepath.EvalSymlinks(filepath.Join(firstGopathWorkspace, "src"))
 				if err != nil {
 					return err
 				}