diff --git a/libavcodec/pnmenc.c b/libavcodec/pnmenc.c
index ba9478d0da..7bb42c5a7a 100644
--- a/libavcodec/pnmenc.c
+++ b/libavcodec/pnmenc.c
@@ -142,6 +142,7 @@ AVCodec ff_pgm_encoder = {
     .pix_fmts       = (const enum AVPixelFormat[]){
         AV_PIX_FMT_GRAY8, AV_PIX_FMT_GRAY16BE, AV_PIX_FMT_NONE
     },
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };
 #endif
 
@@ -156,6 +157,7 @@ AVCodec ff_pgmyuv_encoder = {
     .pix_fmts       = (const enum AVPixelFormat[]){
         AV_PIX_FMT_YUV420P, AV_PIX_FMT_YUV420P16BE, AV_PIX_FMT_NONE
     },
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };
 #endif
 
@@ -170,6 +172,7 @@ AVCodec ff_ppm_encoder = {
     .pix_fmts       = (const enum AVPixelFormat[]){
         AV_PIX_FMT_RGB24, AV_PIX_FMT_RGB48BE, AV_PIX_FMT_NONE
     },
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };
 #endif
 
@@ -183,5 +186,6 @@ AVCodec ff_pbm_encoder = {
     .encode2        = pnm_encode_frame,
     .pix_fmts       = (const enum AVPixelFormat[]){ AV_PIX_FMT_MONOWHITE,
                                                   AV_PIX_FMT_NONE },
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };
 #endif