diff --git a/share/spack/bash/spack-completion.bash b/share/spack/bash/spack-completion.bash
index d779e90aacf9b9..49c691be4c349b 100755
--- a/share/spack/bash/spack-completion.bash
+++ b/share/spack/bash/spack-completion.bash
@@ -367,8 +367,10 @@ _spack_get_alias() {
 # If all commands in COMPREPLY alias to the same thing, set COMPREPLY to
 # just the real command, not the aliases.
 _spack_compress_aliases() {
-    # if there's only one thing, don't bother compressing aliases; complete the alias
-    if [ "${#COMPREPLY[@]}" == "1" ]; then
+    # If there are zero or one completions, don't do anything
+    # If this isn't the first argument, bail because aliases currently only apply
+    # to top-level commands.
+    if [ "${#COMPREPLY[@]}" -le "1" ] || [ "$COMP_CWORD" != "1" ]; then
         return
     fi
 
diff --git a/share/spack/qa/completion-test.sh b/share/spack/qa/completion-test.sh
index 494a1b1235f6df..1071ed36dbeac2 100755
--- a/share/spack/qa/completion-test.sh
+++ b/share/spack/qa/completion-test.sh
@@ -67,6 +67,9 @@ contains 'concretise' _spack_completions spack c
 contains 'concretize' _spack_completions spack conc
 does_not_contain 'concretise' _spack_completions spack conc
 
+does_not_contain 'concretize' _spack_completions spack isnotacommand
+does_not_contain 'concretize' _spack_completions spack env isnotacommand
+
 # XFAIL: Fails for Python 2.6 because pkg_resources not found?
 #contains 'compilers.py' _spack_completions spack unit-test ''
 
diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index e3ddbc45b57ffc..3fb313d8de9122 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -367,8 +367,10 @@ _spack_get_alias() {
 # If all commands in COMPREPLY alias to the same thing, set COMPREPLY to
 # just the real command, not the aliases.
 _spack_compress_aliases() {
-    # if there's only one thing, don't bother compressing aliases; complete the alias
-    if [ "${#COMPREPLY[@]}" == "1" ]; then
+    # If there are zero or one completions, don't do anything
+    # If this isn't the first argument, bail because aliases currently only apply
+    # to top-level commands.
+    if [ "${#COMPREPLY[@]}" -le "1" ] || [ "$COMP_CWORD" != "1" ]; then
         return
     fi