diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index 2f88a1f883..ec74ea4133 100644
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -540,6 +540,30 @@ func runInstall(cmd *Command, args []string) {
 		}
 	}
 	b.do(a)
+	exitIfErrors()
+
+	// Success. If this command is 'go install' with no arguments
+	// and the current directory (the implicit argument) is a command,
+	// remove any leftover command binary from a previous 'go build'.
+	// The binary is installed; it's not needed here anymore.
+	// And worse it might be a stale copy, which you don't want to find
+	// instead of the installed one if $PATH contains dot.
+	// One way to view this behavior is that it is as if 'go install' first
+	// runs 'go build' and the moves the generated file to the install dir.
+	// See issue 9645.
+	if len(args) == 0 && len(pkgs) == 1 && pkgs[0].Name == "main" {
+		// Compute file 'go build' would have created.
+		// If it exists and is an executable file, remove it.
+		_, targ := filepath.Split(pkgs[0].ImportPath)
+		targ += exeSuffix
+		fi, err := os.Stat(targ)
+		if err == nil {
+			m := fi.Mode()
+			if m.IsRegular() && m&0111 != 0 {
+				os.Remove(targ)
+			}
+		}
+	}
 }
 
 // Global build parameters (used during package load)
diff --git a/src/cmd/go/test.bash b/src/cmd/go/test.bash
index 6d4213c738..4f36584de3 100755
--- a/src/cmd/go/test.bash
+++ b/src/cmd/go/test.bash
@@ -96,6 +96,55 @@ elif grep -q runtime $d/err.out; then
 fi
 rm -r $d
 
+TEST 'go install cleans up after go build'
+d=$(TMPDIR=/var/tmp mktemp -d -t testgoXXX)
+export GOPATH=$d
+mkdir -p $d/src/mycmd
+echo 'package main; func main(){}' >$d/src/mycmd/main.go
+old=$(pwd)
+cd $d/src/mycmd
+"$old/testgo" build
+if [ ! -x mycmd ]; then
+	echo "testgo build did not write command binary"
+	ok=false
+fi
+"$old/testgo" install
+if [ -e mycmd ]; then
+	echo "testgo install did not remove command binary"
+	ok=false
+fi
+"$old/testgo" build
+if [ ! -x mycmd ]; then
+	echo "testgo build did not write command binary (second time)"
+	ok=false
+fi
+# install with arguments does not remove the target,
+# even in the same directory
+"$old/testgo" install mycmd
+if [ ! -e mycmd ]; then
+	echo "testgo install mycmd removed command binary when run in mycmd"
+	ok=false
+fi
+"$old/testgo" build
+if [ ! -x mycmd ]; then
+	echo "testgo build did not write command binary (third time)"
+	ok=false
+fi
+# and especially not outside the directory
+cd $d
+cp src/mycmd/mycmd .
+"$old/testgo" install mycmd
+if [ ! -e $d/src/mycmd/mycmd ]; then
+	echo "testgo install mycmd removed command binary from its source dir when run outside mycmd"
+	ok=false
+fi
+if [ ! -e $d/mycmd ]; then
+	echo "testgo install mycmd removed command binary from current dir when run outside mycmd"
+	ok=false
+fi
+cd "$old"
+rm -r $d
+
 TEST 'go install rebuilds stale packages in other GOPATH'
 d=$(TMPDIR=/var/tmp mktemp -d -t testgoXXX)
 export GOPATH=$d/d1:$d/d2