diff --git a/proofs/eo/cpc/Cpc.eo b/proofs/eo/cpc/Cpc.eo
index bd6e9dc58ee..e55143392c3 100644
--- a/proofs/eo/cpc/Cpc.eo
+++ b/proofs/eo/cpc/Cpc.eo
@@ -163,7 +163,7 @@
                                            ))))
       (($run_evaluate (str.prefixof x y)) (eo::define ((ex ($run_evaluate x)))
                                           (eo::define ((ey ($run_evaluate y)))
-                                          (eo::define ((r (eo::find ex ey)))
+                                          (eo::define ((r (eo::find ey ex)))
                                             (eo::ite (eo::is_eq r 0) true
                                             (eo::ite (eo::is_z r) false
                                               (str.prefixof ex ey)))))))
diff --git a/test/regress/cli/CMakeLists.txt b/test/regress/cli/CMakeLists.txt
index f0998ef946b..d18ea82ccc6 100644
--- a/test/regress/cli/CMakeLists.txt
+++ b/test/regress/cli/CMakeLists.txt
@@ -1348,6 +1348,7 @@ set(regress_0_tests
   regress0/proofs/lfsc-test-1.smt2
   regress0/proofs/nomerge-alethe-pf.smt2
   regress0/proofs/no-proof-uc.smt2
+  regress0/proofs/pfcheck_rw_441.smt2
   regress0/proofs/pp-only-proof.smt2
   regress0/proofs/open-pf-datatypes.smt2
   regress0/proofs/open-pf-if-unordered-iff.smt2
diff --git a/test/regress/cli/regress0/proofs/pfcheck_rw_441.smt2 b/test/regress/cli/regress0/proofs/pfcheck_rw_441.smt2
new file mode 100644
index 00000000000..ac5ad1a02e9
--- /dev/null
+++ b/test/regress/cli/regress0/proofs/pfcheck_rw_441.smt2
@@ -0,0 +1,7 @@
+; EXPECT: unsat
+(set-logic QF_SLIA)
+(declare-fun x () String)
+(declare-fun y () String)
+(declare-fun z () Int)
+(assert (not (= (str.prefixof "B" (str.substr x z 0)) false)))
+(check-sat)