diff --git a/bin/crystal b/bin/crystal
index ad5e3357c985..08df2485ee2c 100755
--- a/bin/crystal
+++ b/bin/crystal
@@ -186,6 +186,11 @@ case "$(uname -s)" in
     ;;
 esac
 
+# CRYSTAL_EXEC_PATH determines the location of the `crystal` program for external
+# compiler commands.
+CRYSTAL_EXEC_PATH="$SCRIPT_ROOT"
+export CRYSTAL_EXEC_PATH
+
 if [ -x "$CRYSTAL_DIR/${CRYSTAL_BIN}" ]; then
   __warning_msg "Using compiled compiler at ${CRYSTAL_DIR#"$PWD/"}/${CRYSTAL_BIN}"
   exec "$CRYSTAL_DIR/${CRYSTAL_BIN}" "$@"
diff --git a/spec/primitives/external_command_spec.cr b/spec/primitives/external_command_spec.cr
index 91687f7c2d21..5e9b40a65dfb 100644
--- a/spec/primitives/external_command_spec.cr
+++ b/spec/primitives/external_command_spec.cr
@@ -4,31 +4,36 @@ require "../spec_helper"
 
 describe Crystal::Command do
   it "exec external commands", tags: %w[slow] do
-    with_temp_executable "crystal-external" do |path|
+    with_temp_executable "crystal-external" do |command_path|
+      compiler_path = File.expand_path(ENV["CRYSTAL_SPEC_COMPILER_BIN"]? || "bin/crystal")
+
       with_tempfile "crystal-external.cr" do |source_file|
         File.write source_file, <<-CRYSTAL
-          puts ENV["CRYSTAL"]?
+          puts Process.find_executable("crystal")
           puts PROGRAM_NAME
           puts ARGV
           CRYSTAL
 
-        Process.run(ENV["CRYSTAL_SPEC_COMPILER_BIN"]? || "bin/crystal", ["build", source_file, "-o", path])
+        Process.run(compiler_path, ["build", source_file, "-o", command_path])
       end
 
-      File.exists?(path).should be_true
+      File.exists?(command_path).should be_true
 
-      process = Process.new(ENV["CRYSTAL_SPEC_COMPILER_BIN"]? || "bin/crystal",
+      process = Process.new(compiler_path,
         ["external", "foo", "bar"],
         output: :pipe,
-        env: {"PATH" => {ENV["PATH"], File.dirname(path)}.join(Process::PATH_DELIMITER)}
+        env: {"PATH" => {ENV["PATH"], File.dirname(command_path)}.join(Process::PATH_DELIMITER)}
       )
-      output = process.output.gets_to_end
+      lines = process.output.gets_to_end.lines
+
       status = process.wait
       status.success?.should be_true
-      lines = output.lines
-      lines[0].should match /crystal/
-      lines[1].should match /crystal-external/
-      lines[2].should eq %(["foo", "bar"])
+
+      lines.should eq [
+        compiler_path,
+        command_path,
+        %(["foo", "bar"]),
+      ]
     end
   end
 end
diff --git a/src/compiler/crystal/command.cr b/src/compiler/crystal/command.cr
index 571c965352e0..7c1bf2ff0cb7 100644
--- a/src/compiler/crystal/command.cr
+++ b/src/compiler/crystal/command.cr
@@ -132,7 +132,19 @@ class Crystal::Command
         error "file '#{command}' does not exist"
       elsif external_command = Process.find_executable("crystal-#{command}")
         options.shift
-        Process.exec(external_command, options, env: {"CRYSTAL" => Process.executable_path})
+
+        crystal_exec_path = ENV["CRYSTAL_EXEC_PATH"]?
+        unless crystal_exec_path
+          if executable_path = Process.executable_path
+            crystal_exec_path = File.dirname(executable_path)
+          end
+        end
+        path = [crystal_exec_path, ENV["PATH"]?].compact!.join(Process::PATH_DELIMITER)
+
+        Process.exec(external_command, options, env: {
+          "PATH"              => path,
+          "CRYSTAL_EXEC_PATH" => crystal_exec_path,
+        })
       else
         error "unknown command: #{command}"
       end
diff --git a/src/compiler/crystal/command/spec.cr b/src/compiler/crystal/command/spec.cr
index fd285b653432..69ebbad97caa 100644
--- a/src/compiler/crystal/command/spec.cr
+++ b/src/compiler/crystal/command/spec.cr
@@ -95,7 +95,12 @@ class Crystal::Command
 
     output_filename = Crystal.temp_executable "spec"
 
-    ENV["CRYSTAL_SPEC_COMPILER_BIN"] ||= Process.executable_path
+    ENV["CRYSTAL_SPEC_COMPILER_BIN"] ||= if crystal_exec_path = ENV["CRYSTAL_EXEC_PATH"]?
+                                           File.join(crystal_exec_path, "crystal")
+                                         else
+                                           Process.executable_path
+                                         end
+
     compiler.compile sources, output_filename
     report_warnings
     execute output_filename, options, compiler, error_on_exit: warnings_fail_on_exit?