diff --git a/risu.h b/risu.h
index a7aa929..e6d07eb 100644
--- a/risu.h
+++ b/risu.h
@@ -57,6 +57,14 @@ typedef enum {
     OP_COMPAREMEM = 4,
 } RisuOp;
 
+/* Result of operation */
+typedef enum {
+    RES_OK = 0,
+    RES_END,
+    RES_MISMATCH,
+    RES_BAD_IO,
+} RisuResult;
+
 /* The memory block should be this long */
 #define MEMBLOCKLEN 8192
 
@@ -82,20 +90,21 @@ typedef struct {
  */
 typedef int (*write_fn) (void *ptr, size_t bytes);
 typedef int (*read_fn) (void *ptr, size_t bytes);
-typedef void (*respond_fn) (int response);
+typedef void (*respond_fn) (RisuResult response);
 
-/* Send the register information from the struct ucontext down the socket.
- * Return the response code from the master.
+/*
+ * Send the register information from the struct ucontext down the socket.
  * NB: called from a signal handler.
  */
-int send_register_info(write_fn write_fn, void *uc);
+RisuResult send_register_info(write_fn write_fn, void *uc);
 
-/* Read register info from the socket and compare it with that from the
- * ucontext. Return 0 for match, 1 for end-of-test, 2 for mismatch.
+/*
+ * Read register info from the socket and compare it with that from the
+ * ucontext.
  * NB: called from a signal handler.
  */
-int recv_and_compare_register_info(read_fn read_fn,
-                                   respond_fn respond, void *uc);
+RisuResult recv_and_compare_register_info(read_fn read_fn,
+                                          respond_fn respond, void *uc);
 
 /* Print a useful report on the status of the last comparison
  * done in recv_and_compare_register_info(). This is called on
diff --git a/reginfo.c b/reginfo.c
index 2d67c93..b909a1f 100644
--- a/reginfo.c
+++ b/reginfo.c
@@ -21,7 +21,7 @@ uint8_t apprentice_memblock[MEMBLOCKLEN];
 static int mem_used;
 static int packet_mismatch;
 
-int send_register_info(write_fn write_fn, void *uc)
+RisuResult send_register_info(write_fn write_fn, void *uc)
 {
     struct reginfo ri;
     trace_header_t header;
@@ -34,7 +34,7 @@ int send_register_info(write_fn write_fn, void *uc)
     header.pc = get_pc(&ri);
     header.risu_op = op;
     if (write_fn(&header, sizeof(header)) != 0) {
-        return -1;
+        return RES_BAD_IO;
     }
 
     switch (op) {
@@ -46,10 +46,10 @@ int send_register_info(write_fn write_fn, void *uc)
          * (b) end of test (c) a non-risuop UNDEF
          */
         if (write_fn(&ri, reginfo_size()) != 0) {
-            return -1;
+            return RES_BAD_IO;
         }
         /* For OP_TEST_END, force return 1 to exit. */
-        return op == OP_TESTEND;
+        return op == OP_TESTEND ? RES_END : RES_OK;
     case OP_SETMEMBLOCK:
         memblock = (void *)(uintptr_t)get_reginfo_paramreg(&ri);
         break;
@@ -63,7 +63,7 @@ int send_register_info(write_fn write_fn, void *uc)
     default:
         abort();
     }
-    return 0;
+    return RES_OK;
 }
 
 /* Read register info from the socket and compare it with that from the
@@ -74,10 +74,10 @@ int send_register_info(write_fn write_fn, void *uc)
  * that says whether it is register or memory data, so if the two
  * sides get out of sync then we will fail obscurely.
  */
-int recv_and_compare_register_info(read_fn read_fn,
-                                   respond_fn resp_fn, void *uc)
+RisuResult recv_and_compare_register_info(read_fn read_fn,
+                                          respond_fn resp_fn, void *uc)
 {
-    int resp = 0;
+    RisuResult resp = RES_OK;
     trace_header_t header;
     RisuOp op;
 
@@ -85,18 +85,18 @@ int recv_and_compare_register_info(read_fn read_fn,
     op = get_risuop(&master_ri);
 
     if (read_fn(&header, sizeof(header)) != 0) {
-        return -1;
+        return RES_BAD_IO;
     }
 
     if (header.risu_op != op) {
         /* We are out of sync */
-        resp = 2;
+        resp = RES_BAD_IO;
         resp_fn(resp);
         return resp;
     }
 
     /* send OK for the header */
-    resp_fn(0);
+    resp_fn(RES_OK);
 
     switch (op) {
     case OP_COMPARE:
@@ -107,12 +107,12 @@ int recv_and_compare_register_info(read_fn read_fn,
          */
         if (read_fn(&apprentice_ri, reginfo_size())) {
             packet_mismatch = 1;
-            resp = 2;
+            resp = RES_BAD_IO;
         } else if (!reginfo_is_eq(&master_ri, &apprentice_ri)) {
             /* register mismatch */
-            resp = 2;
+            resp = RES_MISMATCH;
         } else if (op == OP_TESTEND) {
-            resp = 1;
+            resp = RES_END;
         }
         resp_fn(resp);
         break;
@@ -127,10 +127,10 @@ int recv_and_compare_register_info(read_fn read_fn,
         mem_used = 1;
         if (read_fn(apprentice_memblock, MEMBLOCKLEN)) {
             packet_mismatch = 1;
-            resp = 2;
+            resp = RES_BAD_IO;
         } else if (memcmp(memblock, apprentice_memblock, MEMBLOCKLEN) != 0) {
             /* memory mismatch */
-            resp = 2;
+            resp = RES_MISMATCH;
         }
         resp_fn(resp);
         break;
diff --git a/risu.c b/risu.c
index ab17c71..7b14f72 100644
--- a/risu.c
+++ b/risu.c
@@ -69,7 +69,7 @@ int write_trace(void *ptr, size_t bytes)
     return (res == bytes) ? 0 : 1;
 }
 
-void respond_sock(int r)
+void respond_sock(RisuResult r)
 {
     send_response_byte(comm_fd, r);
 }
@@ -98,11 +98,11 @@ int read_trace(void *ptr, size_t bytes)
     return (res == bytes) ? 0 : 1;
 }
 
-void respond_trace(int r)
+void respond_trace(RisuResult r)
 {
     switch (r) {
-    case 0: /* test ok */
-    case 1: /* end of test */
+    case RES_OK:
+    case RES_END:
         break;
     default:
         /* mismatch - if tracing we need to report, otherwise barf */
@@ -115,7 +115,7 @@ void respond_trace(int r)
 
 static void master_sigill(int sig, siginfo_t *si, void *uc)
 {
-    int r;
+    RisuResult r;
     signal_count++;
 
     if (trace) {
@@ -125,7 +125,7 @@ static void master_sigill(int sig, siginfo_t *si, void *uc)
     }
 
     switch (r) {
-    case 0:
+    case RES_OK:
         /* match OK */
         advance_pc(uc);
         return;
@@ -137,7 +137,7 @@ static void master_sigill(int sig, siginfo_t *si, void *uc)
 
 static void apprentice_sigill(int sig, siginfo_t *si, void *uc)
 {
-    int r;
+    RisuResult r;
     signal_count++;
 
     if (trace) {
@@ -147,11 +147,11 @@ static void apprentice_sigill(int sig, siginfo_t *si, void *uc)
     }
 
     switch (r) {
-    case 0:
+    case RES_OK:
         /* match OK */
         advance_pc(uc);
         return;
-    case 1:
+    case RES_END:
         /* end of test */
         exit(EXIT_SUCCESS);
     default:
