diff --git a/src/common b/src/common.sh
similarity index 100%
rename from src/common
rename to src/common.sh
diff --git a/src/expect-core b/src/expect.sh
similarity index 98%
rename from src/expect-core
rename to src/expect.sh
index ee40002..2d44875 100644
--- a/src/expect-core
+++ b/src/expect.sh
@@ -22,7 +22,7 @@
 [ -z $__INC_EXPECT_CORE ] || return
 __INC_EXPECT_CORE=1
 
-source expect/output
+source expect/output.sh
 
 
 ##
diff --git a/src/expect/output b/src/expect/output.sh
similarity index 99%
rename from src/expect/output
rename to src/expect/output.sh
index 58164c5..9cf8044 100644
--- a/src/expect/output
+++ b/src/expect/output.sh
@@ -22,7 +22,7 @@
 [ -z $__INC_EXPECT_OUTPUT ] || return
 __INC_EXPECT_OUTPUT=1
 
-source util
+source util.sh
 
 # reserved for our uses
 exec 99<>/dev/null
diff --git a/src/run-spec b/src/run-spec
index a21ac51..f050946 100755
--- a/src/run-spec
+++ b/src/run-spec
@@ -19,7 +19,7 @@
 #  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 ##
 
-source spec
+source spec.sh
 
 declare -r tcase="${1?Missing test case path}"
 
diff --git a/src/spec b/src/spec.sh
similarity index 99%
rename from src/spec
rename to src/spec.sh
index 9913f11..16cce58 100644
--- a/src/spec
+++ b/src/spec.sh
@@ -29,8 +29,8 @@
 [ -z $__INC_SPEC ] || return
 __INC_SPEC=1
 
-source specstack
-source expect-core
+source specstack.sh
+source expect.sh
 
 # number of internal arguments before remainder clause
 declare -ir __SHIFTN=3
diff --git a/src/specstack b/src/specstack.sh
similarity index 100%
rename from src/specstack
rename to src/specstack.sh
diff --git a/src/util b/src/util.sh
similarity index 100%
rename from src/util
rename to src/util.sh