diff --git a/contrib/jenkins-arm.sh b/contrib/jenkins-arm.sh
index e0c75fa..ef116b1 100755
--- a/contrib/jenkins-arm.sh
+++ b/contrib/jenkins-arm.sh
@@ -2,8 +2,13 @@
 
 . $(dirname "$0")/jenkins_common.sh
 
+src_dir="$PWD"
 build() {
-    $1 --enable-static \
+    build_dir="$1"
+
+    prep_build "$src_dir" "$build_dir"
+
+    "$src_dir"/configure --enable-static \
 	--prefix=/usr/local/arm-none-eabi \
 	--host=arm-none-eabi \
 	--enable-embedded \
@@ -11,15 +16,11 @@
 	--disable-shared \
 	CFLAGS="-Os -ffunction-sections -fdata-sections -nostartfiles -nodefaultlibs -Werror"
 
-$MAKE $PARALLEL_MAKE \
-	|| cat-testlogs.sh
+    $MAKE $PARALLEL_MAKE \
+        || cat-testlogs.sh
 }
 
 # verify build in dir other than source tree
-mkdir -p builddir
-cd builddir
-build ../configure
-
-cd ..
-build ./configure
-
+build builddir
+# verify build in source tree
+build .
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index c397d52..d731504 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -9,19 +9,23 @@
         ENABLE_SANITIZE=""
 fi
 
+src_dir="$PWD"
 build() {
-    $1 --enable-static $2 CFLAGS="-Werror" CPPFLAGS="-Werror"
-$MAKE $PARALLEL_MAKE check \
-  || cat-testlogs.sh
-$MAKE distcheck \
-  || cat-testlogs.sh
+    build_dir="$1"
+
+    prep_build "$src_dir" "$build_dir"
+
+    "$src_dir"/configure --enable-static $ENABLE_SANITIZE CFLAGS="-Werror" CPPFLAGS="-Werror"
+    $MAKE $PARALLEL_MAKE check \
+        || cat-testlogs.sh
 }
 
 # verify build in dir other than source tree
-mkdir -p builddir
-cd builddir
-build ../configure $ENABLE_SANITIZE
+build builddir
+# verify build in source tree
+build .
 
-cd ..
-build ./configure $ENABLE_SANITIZE
-
+# do distcheck only once, which is fine from built source tree, since distcheck
+# is well separated from the source tree state.
+$MAKE distcheck \
+    || cat-testlogs.sh
diff --git a/contrib/jenkins_common.sh b/contrib/jenkins_common.sh
index e52a96a..6cfa334 100644
--- a/contrib/jenkins_common.sh
+++ b/contrib/jenkins_common.sh
@@ -4,4 +4,20 @@
 
 verify_value_string_arrays_are_terminated.py $(find . -name "*.[hc]")
 
-autoreconf --install --force
+prep_build() {
+    _src_dir="$1"
+    _build_dir="$2"
+
+    cd "$_src_dir"
+
+    # a failed 'make distcheck' may leave files without write permissions
+    chmod -R a+w .
+    git clean -dxf
+    # make absolutely sure no src files have modifications
+    git checkout -f HEAD
+
+    autoreconf --install --force
+
+    mkdir -p "$_build_dir"
+    cd "$_build_dir"
+}