diff --git a/docs/maintainers/portfile-functions.md b/docs/maintainers/portfile-functions.md
index 3180609ad0..1aad301eb3 100644
--- a/docs/maintainers/portfile-functions.md
+++ b/docs/maintainers/portfile-functions.md
@@ -16,6 +16,7 @@
 - [vcpkg\_extract\_source\_archive](vcpkg_extract_source_archive.md)
 - [vcpkg\_find\_acquire\_program](vcpkg_find_acquire_program.md)
 - [vcpkg\_from\_bitbucket](vcpkg_from_bitbucket.md)
+- [vcpkg\_from\_git](vcpkg_from_git.md)
 - [vcpkg\_from\_github](vcpkg_from_github.md)
 - [vcpkg\_from\_gitlab](vcpkg_from_gitlab.md)
 - [vcpkg\_install\_cmake](vcpkg_install_cmake.md)
diff --git a/docs/maintainers/vcpkg_from_git.md b/docs/maintainers/vcpkg_from_git.md
new file mode 100644
index 0000000000..6b24a558dd
--- /dev/null
+++ b/docs/maintainers/vcpkg_from_git.md
@@ -0,0 +1,48 @@
+# vcpkg_from_git
+
+Download and extract a project from git
+
+## Usage:
+```cmake
+vcpkg_from_git(
+    OUT_SOURCE_PATH <SOURCE_PATH>
+    URL <https://android.googlesource.com/platform/external/fdlibm>
+    REF <59f7335e4d...>
+    SHA512 <abcdef123...>
+    [PATCHES <patch1.patch> <patch2.patch>...]
+)
+```
+
+## Parameters:
+### OUT_SOURCE_PATH
+Specifies the out-variable that will contain the extracted location.
+
+This should be set to `SOURCE_PATH` by convention.
+
+### URL
+The url of the git repository.
+
+### SHA512
+The SHA512 hash that should match the archive form of the commit.
+
+This is most easily determined by first setting it to `0`, then trying to build the port. The error message will contain the full hash, which can be copied back into the portfile.
+
+### REF
+A stable git commit-ish (ideally a tag or commit) that will not change contents. **This should not be a branch.**
+
+For repositories without official releases, this can be set to the full commit id of the current latest master.
+
+### PATCHES
+A list of patches to be applied to the extracted sources.
+
+Relative paths are based on the port directory.
+
+## Notes:
+`OUT_SOURCE_PATH`, `REF`, `SHA512`, and `URL` must be specified.
+
+## Examples:
+
+* [fdlibm](https://github.com/Microsoft/vcpkg/blob/master/ports/fdlibm/portfile.cmake)
+
+## Source
+[scripts/cmake/vcpkg_from_git.cmake](https://github.com/Microsoft/vcpkg/blob/master/scripts/cmake/vcpkg_from_git.cmake)
diff --git a/scripts/cmake/vcpkg_from_git.cmake b/scripts/cmake/vcpkg_from_git.cmake
index c2965292d0..5f69304120 100644
--- a/scripts/cmake/vcpkg_from_git.cmake
+++ b/scripts/cmake/vcpkg_from_git.cmake
@@ -7,7 +7,8 @@
 ## vcpkg_from_git(
 ##     OUT_SOURCE_PATH <SOURCE_PATH>
 ##     URL <https://android.googlesource.com/platform/external/fdlibm>
-##     [REF <59f7335e4d...>]
+##     REF <59f7335e4d...>
+##     SHA512 <abcdef123...>
 ##     [PATCHES <patch1.patch> <patch2.patch>...]
 ## )
 ## ```
@@ -21,8 +22,15 @@
 ## ### URL
 ## The url of the git repository.
 ##
+## ### SHA512
+## The SHA512 hash that should match the archive form of the commit.
+##
+## This is most easily determined by first setting it to `0`, then trying to build the port. The error message will contain the full hash, which can be copied back into the portfile.
+##
 ## ### REF
-## The full commit id of the current latest master.
+## A stable git commit-ish (ideally a tag or commit) that will not change contents. **This should not be a branch.**
+##
+## For repositories without official releases, this can be set to the full commit id of the current latest master.
 ##
 ## ### PATCHES
 ## A list of patches to be applied to the extracted sources.
@@ -30,7 +38,7 @@
 ## Relative paths are based on the port directory.
 ##
 ## ## Notes:
-## `REF` and `URL` must be specified.
+## `OUT_SOURCE_PATH`, `REF`, `SHA512`, and `URL` must be specified.
 ##
 ## ## Examples:
 ##