diff --git a/Makefile b/Makefile
index 4b028a5f..0fd4be0c 100644
--- a/Makefile
+++ b/Makefile
@@ -46,6 +46,7 @@ help:
 
 .PHONY: test
 test:
+	@echo uname: '$(shell uname)'
 	prove $(prove) $(test)
 
 test-all: test docker-tests
diff --git a/lib/git-subrepo b/lib/git-subrepo
index 546f061a..2776790e 100755
--- a/lib/git-subrepo
+++ b/lib/git-subrepo
@@ -574,7 +574,7 @@ subrepo:pull() {
     fi
   else
     o "Merge in changes from $refs_subrepo_fetch"
-    FAIL=false RUN git merge "$refs_subrepo_fetch"
+    FAIL=false RUN git merge --ff "$refs_subrepo_fetch"
     if ! OK; then
       say "The \"git merge\" command failed:"
       say
diff --git a/test/00-git-config.t b/test/00-git-config.t
new file mode 100644
index 00000000..23b85593
--- /dev/null
+++ b/test/00-git-config.t
@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+
+set -e
+
+source test/setup
+
+use Test::More
+
+note "Define project-wide GIT setup for all tests"
+
+# Get git-subrepo project top directory
+PROJ_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )/.." && pwd )
+
+if [ -z "${PROJ_DIR}" ] || [ "${HOME}" != "${PROJ_DIR}" ]; then
+  is "${HOME}" "${PROJ_DIR}" \
+  "To define project-wide GIT setup for all tests: HOME '${HOME}' should equal PROJ_DIR '${PROJ_DIR}'"
+else
+
+  # Real GIT configuration for tests is set here:
+  rm -f "${PROJ_DIR}/.gitconfig"
+  git config --global user.email "you@example.com"
+  git config --global user.name "Your Name"
+  git config --global init.defaultBranch "master"
+  git config --global --add safe.directory "${PROJ_DIR}"
+  git config --global --add safe.directory "${PROJ_DIR}/.git"
+  git config --global pull.ff only
+  git config --global merge.ff only
+  git config --list
+
+  test-exists "${PROJ_DIR}/.gitconfig"
+
+  # Running tests depends on the whole project being git initialized.
+  # So, git initialize the project, if necessary.
+  if [ ! -d "${PROJ_DIR}/.git" ]; then
+    cd "${PROJ_DIR}"
+    git init .
+    git add .
+    git commit -a -m"Initial commit"
+    cd -
+  fi
+
+  test-exists "${PROJ_DIR}/.git/"
+
+  # Running tests depends on the whole project not being in a GIT detached HEAD state.
+  if ! git symbolic-ref --short --quiet HEAD &> /dev/null; then
+    git checkout -b test
+  fi
+
+  ok "$(
+    git symbolic-ref --short --quiet HEAD &> /dev/null
+  )" "Whole project is not in a GIT detached HEAD state"
+
+fi
+
+done_testing
+
+teardown
diff --git a/test/branch-rev-list-one-path.t b/test/branch-rev-list-one-path.t
index afa49050..575ea8f1 100644
--- a/test/branch-rev-list-one-path.t
+++ b/test/branch-rev-list-one-path.t
@@ -19,7 +19,7 @@ subrepo-clone-bar-into-foo
   add-new-files bar/file3
   add-new-files bar/file4
   add-new-files bar/file5
-  git merge master
+  git merge --ff master
 ) >& /dev/null || die
 
 test-exists "$OWNER/foo/bar/file1" "$OWNER/foo/bar/file2" "$OWNER/foo/bar/file3" "$OWNER/foo/bar/file4" "$OWNER/foo/bar/file5"
diff --git a/test/branch-rev-list.t b/test/branch-rev-list.t
index 243412cd..1f39df42 100644
--- a/test/branch-rev-list.t
+++ b/test/branch-rev-list.t
@@ -22,7 +22,7 @@ subrepo-clone-bar-into-foo
   add-new-files bar/file3
   add-new-files bar/file4
   add-new-files bar/file5
-  git merge master
+  git merge --ff master
 ) >& /dev/null || die
 
 test-exists "$OWNER/foo/bar/file1" "$OWNER/foo/bar/file2" "$OWNER/foo/bar/file3" "$OWNER/foo/bar/file4" "$OWNER/foo/bar/file5"
diff --git a/test/setup b/test/setup
index a05f7ff6..7275c3ee 100644
--- a/test/setup
+++ b/test/setup
@@ -11,6 +11,13 @@ source "$PWD"/.rc
 # Get the location of this script
 SCRIPT_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
 
+# Disable any GIT configuration set outside this 'git-subrepo' project.
+# Real GIT configuration for tests is set through the first test
+# (00-git-config.t).
+export XDG_CONFIG_HOME=$PWD
+export HOME=$PWD
+export GIT_CONFIG_NOSYSTEM=1
+
 BASHLIB=$(
   find "$PWD"/ -type d -name bin -o -type d -name lib | tr '\n' ':'
 )