diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 984571de1f..5cf45e4c18 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -102,6 +102,7 @@ then
   if [[ "$HOMEBREW_MACOS_VERSION_NUMERIC" -lt "100900" ]]
   then
     HOMEBREW_SYSTEM_GIT_TOO_OLD="1"
+    HOMEBREW_FORCE_BREWED_GIT="1"
   fi
 
   if [[ -z "$HOMEBREW_CACHE" ]]
@@ -135,6 +136,15 @@ else
   HOMEBREW_CURL="curl"
 fi
 
+if [[ -n "$HOMEBREW_FORCE_BREWED_GIT" &&
+      -x "$HOMEBREW_PREFIX/opt/git/bin/git" ]] &&
+         "$HOMEBREW_PREFIX/opt/git/bin/git" --version >/dev/null
+then
+  HOMEBREW_GIT="$HOMEBREW_PREFIX/opt/git/bin/git"
+else
+  HOMEBREW_GIT="git"
+fi
+
 HOMEBREW_USER_AGENT="$HOMEBREW_PRODUCT/$HOMEBREW_USER_AGENT_VERSION ($HOMEBREW_SYSTEM; $HOMEBREW_PROCESSOR $HOMEBREW_OS_USER_AGENT_VERSION)"
 HOMEBREW_CURL_VERSION="$("$HOMEBREW_CURL" --version 2>/dev/null | head -n1 | awk '{print $1"/"$2}')"
 HOMEBREW_USER_AGENT_CURL="$HOMEBREW_USER_AGENT $HOMEBREW_CURL_VERSION"
diff --git a/Library/Homebrew/cmd/update.sh b/Library/Homebrew/cmd/update.sh
index d3dae2be31..10668d2596 100644
--- a/Library/Homebrew/cmd/update.sh
+++ b/Library/Homebrew/cmd/update.sh
@@ -384,7 +384,8 @@ EOS
   fi
 
   if ! git --version &>/dev/null ||
-       [[ -n "$HOMEBREW_SYSTEM_GIT_TOO_OLD" &&
+     [[ ( -n "$HOMEBREW_SYSTEM_GIT_TOO_OLD" ||
+          -n "$HOMEBREW_FORCE_BREWED_GIT" ) &&
         ! -x "$HOMEBREW_PREFIX/opt/git/bin/git" ]]
   then
     # we cannot install brewed git if homebrew/core is unavailable.
diff --git a/Library/Homebrew/manpages/brew.1.md.erb b/Library/Homebrew/manpages/brew.1.md.erb
index 100a69d297..902d6bde5b 100644
--- a/Library/Homebrew/manpages/brew.1.md.erb
+++ b/Library/Homebrew/manpages/brew.1.md.erb
@@ -184,6 +184,10 @@ Note that environment variables must have a value set to be detected. For exampl
 
     Set this to force Homebrew to use a particular git binary.
 
+  * `HOMEBREW_FORCE_BREWED_GIT`:
+    If set, Homebrew will use a Homebrew-installed `git` rather than the
+    system version.
+
   * `HOMEBREW_GITHUB_API_TOKEN`:
     A personal access token for the GitHub API, which you can create at
     <https://github.com/settings/tokens>. If set, GitHub will allow you a
diff --git a/docs/Manpage.md b/docs/Manpage.md
index 4666a3999f..9bfc267717 100644
--- a/docs/Manpage.md
+++ b/docs/Manpage.md
@@ -1167,6 +1167,10 @@ Note that environment variables must have a value set to be detected. For exampl
 
     Set this to force Homebrew to use a particular git binary.
 
+  * `HOMEBREW_FORCE_BREWED_GIT`:
+    If set, Homebrew will use a Homebrew-installed `git` rather than the
+    system version.
+
   * `HOMEBREW_GITHUB_API_TOKEN`:
     A personal access token for the GitHub API, which you can create at
     <https://github.com/settings/tokens>. If set, GitHub will allow you a