diff --git a/libexec/pyenv-prefix b/libexec/pyenv-prefix
index a25ff030..9b73795e 100755
--- a/libexec/pyenv-prefix
+++ b/libexec/pyenv-prefix
@@ -30,7 +30,7 @@ OLDIFS="$IFS"
 { IFS=:
   for version in ${PYENV_VERSION}; do
     if [ "$version" = "system" ]; then
-      if PYTHON_PATH="$(pyenv-which python 2>/dev/null)"; then
+      if PYTHON_PATH="$(PYENV_VERSION="${version}" pyenv-which python 2>/dev/null)"; then
         PYENV_PREFIX_PATH="${PYTHON_PATH%/bin/*}"
       else
         echo "pyenv: system version not found in PATH" >&2
diff --git a/test/pyenv_ext.bats b/test/pyenv_ext.bats
index fdc7da46..cc138cbe 100644
--- a/test/pyenv_ext.bats
+++ b/test/pyenv_ext.bats
@@ -1,3 +1,14 @@
 #!/usr/bin/env bats
 
 load test_helper
+
+@test "prefixes" {
+  mkdir -p "${PYENV_TEST_DIR}/bin"
+  touch "${PYENV_TEST_DIR}/bin/python"
+  chmod +x "${PYENV_TEST_DIR}/bin/python"
+  mkdir -p "${PYENV_ROOT}/versions/2.7.10"
+  PYENV_VERSION="system:2.7.10" run pyenv-prefix
+  assert_success "${PYENV_TEST_DIR}:${PYENV_ROOT}/versions/2.7.10"
+  PYENV_VERSION="2.7.10:system" run pyenv-prefix
+  assert_success "${PYENV_ROOT}/versions/2.7.10:${PYENV_TEST_DIR}"
+}