diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index f7d8c60eb61577ce2549edcb923155a118261620..f3f4f02fae6e01d162f8d46574196d78208b9be9 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -333,7 +333,7 @@ impl<'a> DrawingCtx {
                                             node,
                                             &output,
                                             self,
-                                            "2103".as_ptr() as *const i8,
+                                            "2103".as_ptr() as *const libc::c_char,
                                         ))
                                     } else {
                                         None
diff --git a/rsvg_internals/src/filters/ffi.rs b/rsvg_internals/src/filters/ffi.rs
index 8a4e04d730b035195fcd1f44a1ad1da31195488d..3a333cbd0e3824b6a369782ca2db90cf51f9ea78 100644
--- a/rsvg_internals/src/filters/ffi.rs
+++ b/rsvg_internals/src/filters/ffi.rs
@@ -91,7 +91,7 @@ pub fn filter_render(
     let mut channelmap_arr = [0; 4];
     unsafe {
         for i in 0..4 {
-            channelmap_arr[i] = i32::from(*channelmap.offset(i as isize) - '0' as i8);
+            channelmap_arr[i] = i32::from(*channelmap.offset(i as isize) - '0' as c_char);
         }
     }