diff --git a/.github/workflows/build-crate.yml b/.github/workflows/build-crate.yml
index 6c1c14e4..f13eed5c 100644
--- a/.github/workflows/build-crate.yml
+++ b/.github/workflows/build-crate.yml
@@ -8,7 +8,7 @@ on:
 jobs:
 
   build:
-    name: Build crate on ${{ matrix.os }}::${{ matrix.tag}}
+    name: HOST:${{ matrix.os }} DOCK:${{ matrix.tag }}
 
     runs-on: ${{ matrix.os }}
 
@@ -41,7 +41,9 @@ jobs:
     - name: Check out alire-index
       uses: actions/checkout@v2
       with:
-        fetch-depth: 3 # Needed to be able to diff and obtain changed files
+        fetch-depth: 10
+        # Needed to be able to diff and obtain changed files. Changes beyond
+        # that depth are not detected. Should be OK for crate submissions.
 
     - name: Set up GNAT toolchain (FSF)
       if: matrix.os == 'ubuntu-latest'
diff --git a/scripts/gh-build-crate.sh b/scripts/gh-build-crate.sh
index 69d95537..2234c7a7 100755
--- a/scripts/gh-build-crate.sh
+++ b/scripts/gh-build-crate.sh
@@ -6,20 +6,24 @@ trap 'echo "Interrupted" >&2 ; exit 1' INT
 set -o errexit
 set -o nounset
 
-# get changes from second parent of this merge commit
-COMMIT=`git rev-list --parents -n1 HEAD | cut -f3 -d' '`
-echo COMMIT for diff is $COMMIT
-CHANGES=`git diff-tree --no-commit-id --name-only -r $COMMIT`
+# See whats happening
+git log --graph --decorate --pretty=oneline --abbrev-commit --all | head -30
+
+# Detect changes
+CHANGES=$(git diff --name-only HEAD~1)
+
+# Bulk changes for the record
+echo Changed files: $CHANGES
 
 # Import the out-of-docker built alr
 export PATH+=:${PWD}/alire/bin
 
+# Show alr metadata
+alr version
+
 # Configure index
 alr index --name local --add ./index
 
-# Bulk changes for the record
-echo Changed files: $CHANGES
-
 # Test crate
 for file in $CHANGES; do
 
@@ -39,6 +43,7 @@ for file in $CHANGES; do
    fi
 
    # Checks passed, this is a crate we must test
+   list_exes=true # unless it's a system crate
 
    crate=$(basename $file .toml)
    echo Testing crate: $crate
@@ -53,19 +58,68 @@ for file in $CHANGES; do
    alr show --system $crate
    alr show --external --system $crate
    alr show --external-detect --system $crate
+   crateinfo=$(alr show --external-detect --system $crate)
 
-   if $(alr show $crate --system | grep -q 'Available when: False'); then
-      echo Skipping crate build: UNAVAILABLE on system
+   echo CRATE DEPENDENCIES
+   alr show --solve --detail --external-detect $crate
+   solution=$(alr show --solve --detail --external-detect $crate)
+
+   # Skip on explicit unavailability
+   if alr show --system $crate | grep -q 'Available when: False'; then
+      echo SKIPPING crate build: UNAVAILABLE on system
       continue
    fi
 
-   echo BUILDING CRATE
+   # In unsupported platforms, externals are properly reported as missing. We
+   # can skip testing of such a crate since it will likely fail.
+   if grep -q 'Dependencies (external):' <<< $solution ; then
+      echo SKIPPING build for crate with MISSING external dependencies
+      continue
+   fi
+
+   # Update system repositories whenever a detected system package is involved, 
+   # either as dependency or as the crate being tested.
+   if grep -iq 'origin: system' <<< $solution; then
+      echo UPDATING system repositories...
+      type apt-get 2>/dev/null && apt-get update || true
+      type pacman  2>/dev/null && pacman -Syy    || true
+   else
+      echo No need to update system repositories
+   fi
+
+   # Alternatives for when the crate itself comes from an external. Only system
+   # externals should be tested.
+   if grep -q 'Origin: external path' <<< $crateinfo ; then
+      echo SKIPPING detected external crate
+      continue
+   elif grep -q 'Origin: system package' <<< $crateinfo ; then
+      echo INSTALLING detected system crate
+      list_exes=false
+   elif grep -q 'Not found:' <<< $crateinfo && \
+        grep -q 'There are external definitions' <<< $crateinfo
+   then
+      echo SKIPPING undetected external crate
+      continue
+   fi
+
+   # Detect missing dependencies for clearer error
+   if grep -q 'Dependencies cannot be met' <<< $solution ; then
+      echo FAIL: crate dependencies cannot be met
+      exit 1
+   fi
+   
+   # Actual checks
+   echo DEPLOYING CRATE
    alr get --build -n $crate
 
-   echo LISTING EXECUTABLES
-   cd ${crate}_*
-   alr run --list
-   cd ..
+   if $list_exes; then 
+      echo LISTING EXECUTABLES
+      cd ${crate}_*
+      alr run --list
+      cd ..
+   else
+      echo SKIPPING executable listing for system crate
+   fi
 
    echo CRATE BUILD ENDED SUCCESSFULLY
 done