diff --git a/ci/ci_verify_cmake.sh b/ci/ci_verify_cmake.sh
index e3fd529dc..9fe634026 100755
--- a/ci/ci_verify_cmake.sh
+++ b/ci/ci_verify_cmake.sh
@@ -69,6 +69,7 @@ function ci_trace_build {
     ci_info "environment option: \$CI_AR: '$CI_AR'"
     ci_info "environment option: \$CI_RANLIB: '$CI_RANLIB'"
     ci_info "environment option: \$CI_SANITIZERS: '$CI_SANITIZERS'"
+    ci_info "environment option: \$CI_FORCE: '$CI_FORCE'"
     ci_info "environment option: \$CI_NO_TEST: '$CI_NO_TEST'"
     ci_info "environment option: \$CI_NO_INSTALL: '$CI_NO_INSTALL'"
     ci_info "environment option: \$CI_NO_CLEAN: '$CI_NO_CLEAN'"
diff --git a/ci/ci_verify_configure.sh b/ci/ci_verify_configure.sh
index d73e80c26..141c7a283 100755
--- a/ci/ci_verify_configure.sh
+++ b/ci/ci_verify_configure.sh
@@ -57,6 +57,7 @@ function ci_trace_build {
     ci_info "environment option: \$CI_LD: '$CI_LD'"
     ci_info "environment option: \$CI_LD_FLAGS: '$CI_LD_FLAGS'"
     ci_info "environment option: \$CI_SANITIZERS: '$CI_SANITIZERS'"
+    ci_info "environment option: \$CI_FORCE: '$CI_FORCE'"
     ci_info "environment option: \$CI_NO_TEST: '$CI_NO_TEST'"
     ci_info "environment option: \$CI_NO_INSTALL: '$CI_NO_INSTALL'"
     ci_info "environment option: \$CI_NO_CLEAN: '$CI_NO_CLEAN'"
@@ -80,18 +81,29 @@ function ci_trace_build {
 }
 
 function ci_cleanup_old_build {
-    ci_info "## START OF PRE-BUILD CHECKUP ##"
-    ci_spawn test '!' -f "$CI_SRC_DIR/config.status" || {
-        # Warn the user, but do not delete their files.
-        ci_warn "unexpected build configuration file: '$CI_SRC_DIR/config.status'"
-        ci_warn "the configure script might fail"
-    }
-    ci_info "## END OF PRE-BUILD CHECKUP ##"
     ci_info "## START OF PRE-BUILD CLEANUP ##"
     [[ ! -e $CI_BUILD_DIR && ! -e $CI_INSTALL_DIR ]] || {
         ci_spawn rm -fr "$CI_BUILD_DIR"
         ci_spawn rm -fr "$CI_INSTALL_DIR"
     }
+    [[ ! -e "$CI_SRC_DIR/config.status" ]] || {
+        ci_warn "unexpected build configuration file: '$CI_SRC_DIR/config.status'"
+        if ci_expr $((CI_FORCE))
+        then
+            # Delete the old config and (possibly) the old build.
+            ci_info "note: forcing an in-tree build cleanup"
+            if [[ -f $CI_SRC_DIR/Makefile ]]
+            then
+                ci_spawn make -C "$CI_SRC_DIR" distclean
+            else
+                ci_spawn rm -fr "$CI_SRC_DIR"/config.{log,status}
+            fi
+        else
+            # Alert the user, but do not delete their files.
+            ci_warn "the configure script might fail"
+            ci_info "hint: consider using the option \$CI_FORCE=1"
+        fi
+    }
     ci_info "## END OF PRE-BUILD CLEANUP ##"
 }
 
diff --git a/ci/ci_verify_makefiles.sh b/ci/ci_verify_makefiles.sh
index 5b9217ad2..e0681b4d8 100755
--- a/ci/ci_verify_makefiles.sh
+++ b/ci/ci_verify_makefiles.sh
@@ -50,6 +50,7 @@ function ci_trace_build {
     ci_info "environment option: \$CI_LD_FLAGS: '$CI_LD_FLAGS'"
     ci_info "environment option: \$CI_LIBS: '$CI_LIBS'"
     ci_info "environment option: \$CI_SANITIZERS: '$CI_SANITIZERS'"
+    ci_info "environment option: \$CI_FORCE: '$CI_FORCE'"
     ci_info "environment option: \$CI_NO_TEST: '$CI_NO_TEST'"
     ci_info "environment option: \$CI_NO_CLEAN: '$CI_NO_CLEAN'"
     ci_info "executable: \$CI_MAKE: $(command -V "$CI_MAKE")"
@@ -79,13 +80,26 @@ function ci_cleanup_old_build {
     # Fortunately, for a clean makefiles-based build, it should be
     # sufficient to remove the old object files only.
     ci_info "## START OF PRE-BUILD CLEANUP ##"
-    local my_file
-    find "$CI_SRC_DIR" -maxdepth 1 \( -iname "*.o" -o -iname "*.obj" \) |
-        while IFS="" read -r my_file
-        do
-            ci_spawn rm -fr "$my_file"
-        done
-    ci_info "## END OF PRE-BUILD CLEANUP ##"
+    local find_args=(-maxdepth 1 \( -iname "*.o" -o -iname "*.obj" \))
+    [[ ! $(find "$CI_SRC_DIR" "${find_args[@]}" | head -n1) ]] || {
+        ci_warn "unexpected build found in '$CI_SRC_DIR'"
+        if ci_expr $((CI_FORCE))
+        then
+            # Delete the old build.
+            local my_file
+            find "$CI_SRC_DIR" "${find_args[@]}" |
+                while IFS="" read -r my_file
+                do
+                    ci_spawn rm -fr "$my_file"
+                done
+            ci_info "## END OF PRE-BUILD CLEANUP ##"
+        else
+            # Alert the user, but do not delete their existing files,
+            # and do not mess up their existing build.
+            ci_info "hint: consider using the option \$CI_FORCE=1"
+            ci_err "unable to continue"
+        fi
+    }
 }
 
 function ci_build {
diff --git a/ci/lib/ci.lib.sh b/ci/lib/ci.lib.sh
index 813cc09c5..03e866b5c 100644
--- a/ci/lib/ci.lib.sh
+++ b/ci/lib/ci.lib.sh
@@ -88,6 +88,9 @@ function ci_spawn {
 }
 
 # Ensure that the user initialization is correct.
+[[ ${CI_FORCE:-0} == [01] ]] || {
+    ci_err "bad boolean option: \$CI_FORCE: '$CI_FORCE'"
+}
 [[ ${CI_NO_TEST:-0} == [01] ]] || {
     ci_err "bad boolean option: \$CI_NO_TEST: '$CI_NO_TEST'"
 }