diff --git a/bip78/Cargo.toml b/bip78/Cargo.toml
index 901fd8a2..ef9644ab 100644
--- a/bip78/Cargo.toml
+++ b/bip78/Cargo.toml
@@ -23,8 +23,8 @@ base64 = "0.13.0"
 rand = { version = "0.8.4", optional = true }
 bip21 = "0.1.1"
 url = "2.2.2"
+log = { version = "0.4.14", optional = true }
 
 [dev-dependencies]
 bitcoind = { version = "0.18.0", features = ["0_21_1"] }
 env_logger = "0.9.0"
-log = "0.4.14"
diff --git a/bip78/src/lib.rs b/bip78/src/lib.rs
index 82798b34..11cf6752 100644
--- a/bip78/src/lib.rs
+++ b/bip78/src/lib.rs
@@ -37,3 +37,15 @@ pub(crate) mod params;
 pub(crate) mod psbt;
 
 pub use uri::{Uri, PjUri, UriExt, PjUriExt, PjParseError};
+
+#[cfg(feature = "log")]
+macro_rules! log_warn {
+    ($($args:tt)*) => { log::warn!($($args)*) }
+}
+
+#[cfg(not(feature = "log"))]
+macro_rules! log_warn {
+    ($($args:tt)*) => {}
+}
+pub(crate) use log_warn;
+
diff --git a/bip78/src/params.rs b/bip78/src/params.rs
index 2a30de69..01eb8baf 100644
--- a/bip78/src/params.rs
+++ b/bip78/src/params.rs
@@ -1,6 +1,7 @@
 use std::borrow::Borrow;
 use std::fmt;
 
+use crate::log_warn;
 use crate::fee_rate::FeeRate;
 
 #[derive(Debug)]
@@ -44,12 +45,22 @@ impl Params {
                     return Err(ParamsError::UnknownVersion)
                 },
                 ("additionalfeeoutputindex", index) =>  {
-                    if let Ok(index) = index.parse::<usize>() {
-                        additional_fee_output_index = Some(index);
+                    additional_fee_output_index = match index.parse::<usize>() {
+                        Ok(index) => Some(index),
+                        Err(_error) => {
+                            log_warn!("bad `additionalfeeoutputindex` query value '{}': {}", index, _error);
+                            None
+                        }
                     }
                 },
                 ("maxadditionalfeecontribution", fee) => {
-                    max_additional_fee_contribution = bitcoin::Amount::from_str_in(&fee, bitcoin::Denomination::Bitcoin).ok();
+                    max_additional_fee_contribution = match bitcoin::Amount::from_str_in(&fee, bitcoin::Denomination::Bitcoin) {
+                        Ok(contribution) => Some(contribution),
+                        Err(_error) => {
+                            log_warn!("bad `maxadditionalfeecontribution` query value '{}': {}", fee, _error);
+                            None
+                        }
+                    }
                 }
                 ("minfeerate", feerate) => {
                     params.min_feerate = match feerate.parse::<u64>() {
@@ -57,12 +68,15 @@ impl Params {
                         Err(e) => return Err(ParamsError::FeeRate(e)),
                     }
                 }
-                ("disableoutputsubstitution", v) => params.disable_output_substitution = v == "true", // existance is truthy
+                ("disableoutputsubstitution", v) => params.disable_output_substitution = v == "true",
                 _ => (),
             }
         }
-        if let (Some(amount), Some(index)) = (max_additional_fee_contribution, additional_fee_output_index) {
-            params.additional_fee_contribution = Some((amount, index));
+
+        match (max_additional_fee_contribution, additional_fee_output_index) {
+            (Some(amount), Some(index)) => params.additional_fee_contribution = Some((amount, index)),
+            (Some(_), None) | (None, Some(_)) => { log_warn!("only one additional-fee parameter specified: {:?}", params); },
+            _ => ()
         }
 
         Ok(params)