diff --git a/src/core/channel/call_op_string.c b/src/core/channel/call_op_string.c
index 4f19d021d5e..d36d51e7896 100644
--- a/src/core/channel/call_op_string.c
+++ b/src/core/channel/call_op_string.c
@@ -117,7 +117,7 @@ char *grpc_call_op_string(grpc_call_op *op) {
   gpr_asprintf(&tmp, " flags=0x%08x", op->flags);
   gpr_strvec_add(&b, tmp);
 
-  out = gpr_strvec_flatten(&b);
+  out = gpr_strvec_flatten(&b, NULL);
   gpr_strvec_destroy(&b);
 
   return out;
diff --git a/src/core/support/string.c b/src/core/support/string.c
index 87c2cd351b0..008b2aac899 100644
--- a/src/core/support/string.c
+++ b/src/core/support/string.c
@@ -153,7 +153,7 @@ int gpr_ltoa(long value, char *string) {
   return i;
 }
 
-char *gpr_strjoin(const char **strs, size_t nstrs) {
+char *gpr_strjoin(const char **strs, size_t nstrs, size_t *final_length) {
   size_t out_length = 0;
   size_t i;
   char *out;
@@ -169,6 +169,9 @@ char *gpr_strjoin(const char **strs, size_t nstrs) {
     out_length += slen;
   }
   out[out_length] = 0;
+  if (final_length != NULL) {
+    *final_length = out_length;
+  }
   return out;
 }
 
@@ -192,6 +195,6 @@ void gpr_strvec_add(gpr_strvec *sv, char *str) {
   sv->strs[sv->count++] = str;
 }
 
-char *gpr_strvec_flatten(gpr_strvec *sv) {
-  return gpr_strjoin((const char**)sv->strs, sv->count);
+char *gpr_strvec_flatten(gpr_strvec *sv, size_t *final_length) {
+  return gpr_strjoin((const char**)sv->strs, sv->count, final_length);
 }
diff --git a/src/core/support/string.h b/src/core/support/string.h
index 98c66b14e2d..d8fd2638ef8 100644
--- a/src/core/support/string.h
+++ b/src/core/support/string.h
@@ -81,8 +81,10 @@ void gpr_reverse_bytes(char *str, int len);
    the result is undefined. */
 int gpr_asprintf(char **strp, const char *format, ...);
 
-/* Join a set of strings, returning the resulting string */
-char *gpr_strjoin(const char **strs, size_t nstrs);
+/* Join a set of strings, returning the resulting string.
+   Total combined length (excluding null terminator) is returned in total_length
+   if it is non-null. */
+char *gpr_strjoin(const char **strs, size_t nstrs, size_t *total_length);
 
 /* A vector of strings... addition takes ownership of strings */
 typedef struct {
@@ -94,7 +96,7 @@ typedef struct {
 void gpr_strvec_init(gpr_strvec *strs);
 void gpr_strvec_destroy(gpr_strvec *strs);
 void gpr_strvec_add(gpr_strvec *strs, char *add);
-char *gpr_strvec_flatten(gpr_strvec *strs);
+char *gpr_strvec_flatten(gpr_strvec *strs, size_t *total_length);
 
 #ifdef __cplusplus
 }
diff --git a/src/core/surface/event_string.c b/src/core/surface/event_string.c
index 5a71cdadaba..8975d312eec 100644
--- a/src/core/surface/event_string.c
+++ b/src/core/surface/event_string.c
@@ -131,7 +131,7 @@ char *grpc_event_string(grpc_event *ev) {
       break;
   }
 
-  out = gpr_strvec_flatten(&buf);
+  out = gpr_strvec_flatten(&buf, NULL);
   gpr_strvec_destroy(&buf);
   return out;
 }