diff --git a/third_party/build/ilbc/notes.txt b/third_party/build/ilbc/notes.txt
new file mode 100644
index 000000000..bcea32031
--- /dev/null
+++ b/third_party/build/ilbc/notes.txt
@@ -0,0 +1,5 @@
+Notes:
+* Modify iLBC_decode.c and iLBC_encode.c
+  - iLBC using memcpy instead of memmove for overlapping memory. This will 
+    cause some weird sound if the call lasted longer than ~30s. To fix this,
+    some call to memcpy is changed to memmove. Have a look at #2116.
diff --git a/third_party/ilbc/iLBC_decode.c b/third_party/ilbc/iLBC_decode.c
index 17395d3a9..ea7d7ee21 100644
--- a/third_party/ilbc/iLBC_decode.c
+++ b/third_party/ilbc/iLBC_decode.c
@@ -251,7 +251,7 @@
 
                /* update memory */
 
-               memcpy(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
+               memmove(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
                memcpy(mem+CB_MEML-SUBL,
 
 
@@ -299,7 +299,7 @@
 
                /* update memory */
 
-               memcpy(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
+               memmove(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
                memcpy(mem+CB_MEML-SUBL,
                    &reverseDecresidual[subframe*SUBL],
                    SUBL*sizeof(float));
diff --git a/third_party/ilbc/iLBC_encode.c b/third_party/ilbc/iLBC_encode.c
index 438545883..4e19dc19e 100644
--- a/third_party/ilbc/iLBC_encode.c
+++ b/third_party/ilbc/iLBC_encode.c
@@ -308,7 +308,7 @@
 
                /* update memory */
 
-               memcpy(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
+               memmove(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
                memcpy(mem+CB_MEML-SUBL,
 
 
@@ -386,7 +386,7 @@
 
                /* update memory */
 
-               memcpy(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
+               memmove(mem, mem+SUBL, (CB_MEML-SUBL)*sizeof(float));
                memcpy(mem+CB_MEML-SUBL,
                    &reverseDecresidual[subframe*SUBL],
                    SUBL*sizeof(float));