diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
index 456ac9ccf1933daa2e3d3f50e124b95d2940ad27..3d8d08ac37a0c23016d1c588c359864936aa6dce 100644
--- a/libavfilter/avfilter.c
+++ b/libavfilter/avfilter.c
@@ -205,7 +205,7 @@ int avfilter_config_links(AVFilterContext *filter)
     return 0;
 }
 
-char *ff_get_ref_perms_string(char *buf, size_t buf_size, int perms)
+static char *ff_get_ref_perms_string(char *buf, size_t buf_size, int perms)
 {
     snprintf(buf, buf_size, "%s%s%s%s%s%s",
              perms & AV_PERM_READ      ? "r" : "",
@@ -217,7 +217,7 @@ char *ff_get_ref_perms_string(char *buf, size_t buf_size, int perms)
     return buf;
 }
 
-void ff_dprintf_ref(void *ctx, AVFilterBufferRef *ref, int end)
+static void ff_dprintf_ref(void *ctx, AVFilterBufferRef *ref, int end)
 {
     av_unused char buf[16];
     dprintf(ctx,
@@ -245,7 +245,7 @@ void ff_dprintf_ref(void *ctx, AVFilterBufferRef *ref, int end)
     dprintf(ctx, "]%s", end ? "\n" : "");
 }
 
-void ff_dprintf_link(void *ctx, AVFilterLink *link, int end)
+static void ff_dprintf_link(void *ctx, AVFilterLink *link, int end)
 {
     if (link->type == AVMEDIA_TYPE_VIDEO) {
         dprintf(ctx,
@@ -269,6 +269,8 @@ void ff_dprintf_link(void *ctx, AVFilterLink *link, int end)
     }
 }
 
+#define FF_DPRINTF_START(ctx, func) dprintf(NULL, "%-16s: ", #func)
+
 AVFilterBufferRef *avfilter_get_video_buffer(AVFilterLink *link, int perms, int w, int h)
 {
     AVFilterBufferRef *ret = NULL;
diff --git a/libavfilter/internal.h b/libavfilter/internal.h
index 8f352ef775358a4c8ab7cb99828259b65012dbad..188da8709992946bc2d9d50a5dceeb8ba81c68d1 100644
--- a/libavfilter/internal.h
+++ b/libavfilter/internal.h
@@ -27,14 +27,6 @@
 #include "avfilter.h"
 #include "avfiltergraph.h"
 
-void ff_dprintf_ref(void *ctx, AVFilterBufferRef *ref, int end);
-
-char *ff_get_ref_perms_string(char *buf, size_t buf_size, int perms);
-
-void ff_dprintf_link(void *ctx, AVFilterLink *link, int end);
-
-#define FF_DPRINTF_START(ctx, func) dprintf(NULL, "%-16s: ", #func)
-
 /**
  * Check for the validity of graph.
  *