diff --git a/src/modules/audio_processing/ns/ns_core.c b/src/modules/audio_processing/ns/ns_core.c
index 791d4197b..e80f699c5 100644
--- a/src/modules/audio_processing/ns/ns_core.c
+++ b/src/modules/audio_processing/ns/ns_core.c
@@ -111,7 +111,7 @@ int WebRtcNs_InitCore(NSinst_t* inst, WebRtc_UWord32 fs) {
   // Initialize fft work arrays.
   inst->ip[0] = 0; // Setting this triggers initialization.
   memset(inst->dataBuf, 0, sizeof(float) * ANAL_BLOCKL_MAX);
-  rdft(inst->anaLen, 1, inst->dataBuf, inst->ip, inst->wfft);
+  WebRtc_rdft(inst->anaLen, 1, inst->dataBuf, inst->ip, inst->wfft);
 
   memset(inst->dataBuf, 0, sizeof(float) * ANAL_BLOCKL_MAX);
   memset(inst->syntBuf, 0, sizeof(float) * ANAL_BLOCKL_MAX);
@@ -862,7 +862,7 @@ int WebRtcNs_ProcessCore(NSinst_t* inst,
     //
     inst->blockInd++; // Update the block index only when we process a block.
     // FFT
-    rdft(inst->anaLen, 1, winData, inst->ip, inst->wfft);
+    WebRtc_rdft(inst->anaLen, 1, winData, inst->ip, inst->wfft);
 
     imag[0] = 0;
     real[0] = winData[0];
@@ -1155,7 +1155,7 @@ int WebRtcNs_ProcessCore(NSinst_t* inst,
       winData[2 * i] = real[i];
       winData[2 * i + 1] = imag[i];
     }
-    rdft(inst->anaLen, -1, winData, inst->ip, inst->wfft);
+    WebRtc_rdft(inst->anaLen, -1, winData, inst->ip, inst->wfft);
 
     for (i = 0; i < inst->anaLen; i++) {
       real[i] = 2.0f * winData[i] / inst->anaLen; // fft scaling
diff --git a/src/modules/audio_processing/utility/fft4g.c b/src/modules/audio_processing/utility/fft4g.c
index 9a84368c4..cbc4dc31e 100644
--- a/src/modules/audio_processing/utility/fft4g.c
+++ b/src/modules/audio_processing/utility/fft4g.c
@@ -286,14 +286,24 @@ Appendix :
     w[] and ip[] are compatible with all routines.
 */
 
-void cdft(int n, int isgn, float *a, int *ip, float *w)
-{
-    void makewt(int nw, int *ip, float *w);
-    void bitrv2(int n, int *ip, float *a);
-    void bitrv2conj(int n, int *ip, float *a);
-    void cftfsub(int n, float *a, float *w);
-    void cftbsub(int n, float *a, float *w);
+static void makewt(int nw, int *ip, float *w);
+static void makect(int nc, int *ip, float *c);
+static void bitrv2(int n, int *ip, float *a);
+static void bitrv2conj(int n, int *ip, float *a);
+static void cftfsub(int n, float *a, float *w);
+static void cftbsub(int n, float *a, float *w);
+static void cft1st(int n, float *a, float *w);
+static void cftmdl(int n, int l, float *a, float *w);
+static void rftfsub(int n, float *a, int nc, float *c);
+static void rftbsub(int n, float *a, int nc, float *c);
+#if 0  // Not used.
+static void dctsub(int n, float *a, int nc, float *c)
+static void dstsub(int n, float *a, int nc, float *c)
+#endif
 
+
+void WebRtc_cdft(int n, int isgn, float *a, int *ip, float *w)
+{
     if (n > (ip[0] << 2)) {
         makewt(n >> 2, ip, w);
     }
@@ -311,15 +321,8 @@ void cdft(int n, int isgn, float *a, int *ip, float *w)
 }
 
 
-void rdft(int n, int isgn, float *a, int *ip, float *w)
+void WebRtc_rdft(int n, int isgn, float *a, int *ip, float *w)
 {
-    void makewt(int nw, int *ip, float *w);
-    void makect(int nc, int *ip, float *c);
-    void bitrv2(int n, int *ip, float *a);
-    void cftfsub(int n, float *a, float *w);
-    void cftbsub(int n, float *a, float *w);
-    void rftfsub(int n, float *a, int nc, float *c);
-    void rftbsub(int n, float *a, int nc, float *c);
     int nw, nc;
     float xi;
 
@@ -357,17 +360,9 @@ void rdft(int n, int isgn, float *a, int *ip, float *w)
     }
 }
 
-
-void ddct(int n, int isgn, float *a, int *ip, float *w)
+#if 0  // Not used.
+static void ddct(int n, int isgn, float *a, int *ip, float *w)
 {
-    void makewt(int nw, int *ip, float *w);
-    void makect(int nc, int *ip, float *c);
-    void bitrv2(int n, int *ip, float *a);
-    void cftfsub(int n, float *a, float *w);
-    void cftbsub(int n, float *a, float *w);
-    void rftfsub(int n, float *a, int nc, float *c);
-    void rftbsub(int n, float *a, int nc, float *c);
-    void dctsub(int n, float *a, int nc, float *c);
     int j, nw, nc;
     float xr;
 
@@ -417,16 +412,8 @@ void ddct(int n, int isgn, float *a, int *ip, float *w)
 }
 
 
-void ddst(int n, int isgn, float *a, int *ip, float *w)
+static void ddst(int n, int isgn, float *a, int *ip, float *w)
 {
-    void makewt(int nw, int *ip, float *w);
-    void makect(int nc, int *ip, float *c);
-    void bitrv2(int n, int *ip, float *a);
-    void cftfsub(int n, float *a, float *w);
-    void cftbsub(int n, float *a, float *w);
-    void rftfsub(int n, float *a, int nc, float *c);
-    void rftbsub(int n, float *a, int nc, float *c);
-    void dstsub(int n, float *a, int nc, float *c);
     int j, nw, nc;
     float xr;
 
@@ -476,14 +463,8 @@ void ddst(int n, int isgn, float *a, int *ip, float *w)
 }
 
 
-void dfct(int n, float *a, float *t, int *ip, float *w)
+static void dfct(int n, float *a, float *t, int *ip, float *w)
 {
-    void makewt(int nw, int *ip, float *w);
-    void makect(int nc, int *ip, float *c);
-    void bitrv2(int n, int *ip, float *a);
-    void cftfsub(int n, float *a, float *w);
-    void rftfsub(int n, float *a, int nc, float *c);
-    void dctsub(int n, float *a, int nc, float *c);
     int j, k, l, m, mh, nw, nc;
     float xr, xi, yr, yi;
 
@@ -571,15 +552,8 @@ void dfct(int n, float *a, float *t, int *ip, float *w)
     }
 }
 
-
-void dfst(int n, float *a, float *t, int *ip, float *w)
+static void dfst(int n, float *a, float *t, int *ip, float *w)
 {
-    void makewt(int nw, int *ip, float *w);
-    void makect(int nc, int *ip, float *c);
-    void bitrv2(int n, int *ip, float *a);
-    void cftfsub(int n, float *a, float *w);
-    void rftfsub(int n, float *a, int nc, float *c);
-    void dstsub(int n, float *a, int nc, float *c);
     int j, k, l, m, mh, nw, nc;
     float xr, xi, yr, yi;
 
@@ -657,6 +631,7 @@ void dfst(int n, float *a, float *t, int *ip, float *w)
     }
     a[0] = 0;
 }
+#endif  // Not used.
 
 
 /* -------- initializing routines -------- */
@@ -664,9 +639,8 @@ void dfst(int n, float *a, float *t, int *ip, float *w)
 
 #include <math.h>
 
-void makewt(int nw, int *ip, float *w)
+static void makewt(int nw, int *ip, float *w)
 {
-    void bitrv2(int n, int *ip, float *a);
     int j, nwh;
     float delta, x, y;
 
@@ -694,7 +668,7 @@ void makewt(int nw, int *ip, float *w)
 }
 
 
-void makect(int nc, int *ip, float *c)
+static void makect(int nc, int *ip, float *c)
 {
     int j, nch;
     float delta;
@@ -716,7 +690,7 @@ void makect(int nc, int *ip, float *c)
 /* -------- child routines -------- */
 
 
-void bitrv2(int n, int *ip, float *a)
+static void bitrv2(int n, int *ip, float *a)
 {
     int j, j1, k, k1, l, m, m2;
     float xr, xi, yr, yi;
@@ -816,7 +790,7 @@ void bitrv2(int n, int *ip, float *a)
 }
 
 
-void bitrv2conj(int n, int *ip, float *a)
+static void bitrv2conj(int n, int *ip, float *a)
 {
     int j, j1, k, k1, l, m, m2;
     float xr, xi, yr, yi;
@@ -925,10 +899,8 @@ void bitrv2conj(int n, int *ip, float *a)
 }
 
 
-void cftfsub(int n, float *a, float *w)
+static void cftfsub(int n, float *a, float *w)
 {
-    void cft1st(int n, float *a, float *w);
-    void cftmdl(int n, int l, float *a, float *w);
     int j, j1, j2, j3, l;
     float x0r, x0i, x1r, x1i, x2r, x2i, x3r, x3i;
 
@@ -977,10 +949,8 @@ void cftfsub(int n, float *a, float *w)
 }
 
 
-void cftbsub(int n, float *a, float *w)
+static void cftbsub(int n, float *a, float *w)
 {
-    void cft1st(int n, float *a, float *w);
-    void cftmdl(int n, int l, float *a, float *w);
     int j, j1, j2, j3, l;
     float x0r, x0i, x1r, x1i, x2r, x2i, x3r, x3i;
 
@@ -1029,7 +999,7 @@ void cftbsub(int n, float *a, float *w)
 }
 
 
-void cft1st(int n, float *a, float *w)
+static void cft1st(int n, float *a, float *w)
 {
     int j, k1, k2;
     float wk1r, wk1i, wk2r, wk2i, wk3r, wk3i;
@@ -1134,7 +1104,7 @@ void cft1st(int n, float *a, float *w)
 }
 
 
-void cftmdl(int n, int l, float *a, float *w)
+static void cftmdl(int n, int l, float *a, float *w)
 {
     int j, j1, j2, j3, k, k1, k2, m, m2;
     float wk1r, wk1i, wk2r, wk2i, wk3r, wk3i;
@@ -1261,7 +1231,7 @@ void cftmdl(int n, int l, float *a, float *w)
 }
 
 
-void rftfsub(int n, float *a, int nc, float *c)
+static void rftfsub(int n, float *a, int nc, float *c)
 {
     int j, k, kk, ks, m;
     float wkr, wki, xr, xi, yr, yi;
@@ -1286,7 +1256,7 @@ void rftfsub(int n, float *a, int nc, float *c)
 }
 
 
-void rftbsub(int n, float *a, int nc, float *c)
+static void rftbsub(int n, float *a, int nc, float *c)
 {
     int j, k, kk, ks, m;
     float wkr, wki, xr, xi, yr, yi;
@@ -1312,8 +1282,8 @@ void rftbsub(int n, float *a, int nc, float *c)
     a[m + 1] = -a[m + 1];
 }
 
-
-void dctsub(int n, float *a, int nc, float *c)
+#if 0  // Not used.
+static void dctsub(int n, float *a, int nc, float *c)
 {
     int j, k, kk, ks, m;
     float wkr, wki, xr;
@@ -1334,7 +1304,7 @@ void dctsub(int n, float *a, int nc, float *c)
 }
 
 
-void dstsub(int n, float *a, int nc, float *c)
+static void dstsub(int n, float *a, int nc, float *c)
 {
     int j, k, kk, ks, m;
     float wkr, wki, xr;
@@ -1353,4 +1323,4 @@ void dstsub(int n, float *a, int nc, float *c)
     }
     a[m] *= c[0];
 }
-
+#endif  // Not used.
diff --git a/src/modules/audio_processing/utility/fft4g.h b/src/modules/audio_processing/utility/fft4g.h
index 373ff1489..14a52a106 100644
--- a/src/modules/audio_processing/utility/fft4g.h
+++ b/src/modules/audio_processing/utility/fft4g.h
@@ -11,8 +11,7 @@
 #ifndef WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_FFT4G_H_
 #define WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_FFT4G_H_
 
-void rdft(int, int, float *, int *, float *);
-void cdft(int, int, float *, int *, float *);
+void WebRtc_rdft(int, int, float *, int *, float *);
+void WebRtc_cdft(int, int, float *, int *, float *);
 
 #endif
-