diff --git a/rostests/apitests/crt/strlen.c b/rostests/apitests/crt/strlen.c
index ed88c048ec6..84345c16127 100644
--- a/rostests/apitests/crt/strlen.c
+++ b/rostests/apitests/crt/strlen.c
@@ -23,12 +23,18 @@ GCC_builtin_strlen(const char *str)
 }
 #endif
 
+#define EFLAGS_DF 0x400L
+
 typedef size_t (*PFN_STRLEN)(const char *);
 
 void
 Test_strlen(PFN_STRLEN pstrlen)
 {
     size_t len;
+#if defined(_M_IX86) || defined(_M_AMD64)
+    volatile uintptr_t eflags;
+    char *teststr = "a\0bcdefghijk";
+#endif
 
     /* basic parameter tests */
     StartSeh()
@@ -37,6 +43,21 @@ Test_strlen(PFN_STRLEN pstrlen)
     (void)len;
 
     ok_int((int)pstrlen("test"), 4);
+
+#if defined(_M_IX86) || defined(_M_AMD64)
+    eflags = __readeflags();
+    __writeeflags(eflags | EFLAGS_DF);
+    len = pstrlen(teststr + 4);
+    eflags = __readeflags();
+    ok((eflags & EFLAGS_DF) != 0, "Direction flag in ELFAGS was changed.");
+
+    /* Only test this for the exported versions, intrinsics might do it
+       differently. It's up to us to not do fishy stuff! */
+    if (pstrlen == strlen)
+    {
+        ok(len == 8, "Should not have gone backwards (got len %i)", (int)len);
+    }
+#endif
 }
 
 START_TEST(strlen)