diff --git a/groth16/files/container.nim b/groth16/files/container.nim
index 28e2a0d..208b853 100644
--- a/groth16/files/container.nim
+++ b/groth16/files/container.nim
@@ -61,8 +61,8 @@ proc readSection[T] ( expectedMagic: string
                     , stream: Stream
                     , user: var T
                     , callback: SectionCallback[T] 
-                    , filt: proc(_: int): bool {.raises: [IOError, OSError].}
-                    ) {.raises: [IOError, OSError].} =
+                    , filt: proc(_: int): bool {.gcsafe, raises: [IOError, OSError].}
+                    ) {.gcsafe, raises: [IOError, OSError].} =
 
   let sectId  = int( stream.readUint32() )
   let sectLen = int( stream.readUint64() )
@@ -78,7 +78,7 @@ proc parseContainer*[T] ( expectedMagic: string
                         , fname: string
                         , user: var T
                         , callback: SectionCallback[T] 
-                        , filt: proc(_: int): bool {.raises: [IOError, OSError].}
+                        , filt: proc(_: int): bool {.gcsafe, raises: [IOError, OSError].}
                         ) {.raises: [IOError, OSError].} =
 
   let stream = newFileStream(fname, mode = fmRead)
diff --git a/groth16/files/zkey.nim b/groth16/files/zkey.nim
index 8ee4129..2da39f4 100644
--- a/groth16/files/zkey.nim
+++ b/groth16/files/zkey.nim
@@ -238,7 +238,7 @@ proc zkeyCallback(stream: Stream, sectId: int, sectLen: int, user: var ZKey) =
     of 9: parseSection9_PointsH1(    stream, user, sectLen )
     else: discard
 
-proc parseZKey* (fname: string): ZKey = 
+proc parseZKey* (fname: string): ZKey {.gcsafe.} = 
   var zkey : ZKey
   parseContainer( "zkey", 1, fname, zkey, zkeyCallback, proc (id: int): bool = id == 1 )
   parseContainer( "zkey", 1, fname, zkey, zkeyCallback, proc (id: int): bool = id == 2 )