diff --git a/TODO.FACTOR.txt b/TODO.FACTOR.txt
index 47916b3e91..9733f8c6e5 100644
--- a/TODO.FACTOR.txt
+++ b/TODO.FACTOR.txt
@@ -33,6 +33,7 @@
 - utf16 string boxing
 - slot compile problem
 - nulls at the end of utf16 strings
+- x86 register decl
 
 + compiler/ffi:
 
diff --git a/library/bootstrap/image.factor b/library/bootstrap/image.factor
index b5337eb04f..7f0f21ff48 100644
--- a/library/bootstrap/image.factor
+++ b/library/bootstrap/image.factor
@@ -253,7 +253,7 @@ M: cons ' ( c -- tagged )
     string-type >header emit
     dup str-length emit
     dup hashcode emit-fixnum
-    pack-string
+    "\0" cat2 pack-string
     align-here ;
 
 M: string ' ( string -- pointer )
diff --git a/native/factor.h b/native/factor.h
index c880678c64..08c7259fab 100644
--- a/native/factor.h
+++ b/native/factor.h
@@ -27,6 +27,9 @@ CELL cs_bot;
 /* raw pointer to callstack top */
 DLLEXPORT CELL cs;
 
+/* TAGGED currently executing quotation */
+CELL callframe;
+
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
diff --git a/native/run.h b/native/run.h
index 7331bf5f68..1461354704 100644
--- a/native/run.h
+++ b/native/run.h
@@ -26,9 +26,6 @@ jmp_buf toplevel;
 sigjmp_buf toplevel;
 #endif
 
-/* TAGGED currently executing quotation */
-CELL callframe;
-
 /* TAGGED pointer to currently executing word */
 CELL executing;
 
diff --git a/native/string.c b/native/string.c
index e5a88bd7a5..be8547722b 100644
--- a/native/string.c
+++ b/native/string.c
@@ -4,7 +4,12 @@
 F_STRING* allot_string(CELL capacity)
 {
 	F_STRING* string = allot_object(STRING_TYPE,
-		sizeof(F_STRING) + capacity * CHARS);
+		sizeof(F_STRING) + (capacity + 1) * CHARS);
+	/* strings are null-terminated in memory, even though they also
+	have a length field. The null termination allows us to add
+	the sizeof(F_STRING) to a Factor string to get a C-style
+	UTF16 string for C library calls. */
+	cput(SREF(string,capacity),(uint16_t)'\0');
 	string->capacity = capacity;
 	return string;
 }
diff --git a/native/string.h b/native/string.h
index 1087193118..6f06c7f50e 100644
--- a/native/string.h
+++ b/native/string.h
@@ -1,11 +1,18 @@
+
+
 typedef struct {
 	CELL header;
-	/* untagged */
+	/* untagged num of chars */
 	CELL capacity;
 	/* tagged */
 	CELL hashcode;
 } F_STRING;
 
+#define SREF(string,index) ((CELL)string + sizeof(F_STRING) + index * CHARS)
+
+#define SSIZE(pointer) align8(sizeof(F_STRING) + \
+	(((F_STRING*)pointer)->capacity + 1) * CHARS)
+
 INLINE F_STRING* untag_string(CELL tagged)
 {
 	type_check(STRING_TYPE,tagged);
@@ -26,11 +33,6 @@ void primitive_memory_to_string(void);
 DLLEXPORT BYTE* unbox_c_string(void);
 DLLEXPORT uint16_t* unbox_utf16_string(void);
 
-#define SREF(string,index) ((CELL)string + sizeof(F_STRING) + index * CHARS)
-
-#define SSIZE(pointer) align8(sizeof(F_STRING) + \
-	((F_STRING*)pointer)->capacity * CHARS)
-
 /* untagged & unchecked */
 INLINE CELL string_nth(F_STRING* string, CELL index)
 {