diff --git a/Cargo.lock b/Cargo.lock
index 9fd0b7a97..eaf43d58e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -624,7 +624,7 @@ dependencies = [
  "escaper 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "failure_derive 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "image-meta 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "jetscii 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1112,11 +1112,6 @@ dependencies = [
  "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "hex"
-version = "0.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "hex"
 version = "0.4.0"
@@ -1538,7 +1533,7 @@ version = "0.1.2"
 dependencies = [
  "charset 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "chrono 0.4.9 (registry+https://github.com/rust-lang/crates.io-index)",
- "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
  "memmap 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3377,7 +3372,6 @@ dependencies = [
 "checksum h2 0.1.26 (registry+https://github.com/rust-lang/crates.io-index)" = "a5b34c246847f938a410a03c5458c7fee2274436675e76d8b903c08efc29c462"
 "checksum heck 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "20564e78d53d2bb135c343b3f47714a56af2061f1c928fdb541dc7b9fdd94205"
 "checksum hermit-abi 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "307c3c9f937f38e3534b1d6447ecf090cafcc9744e4a6360e8b037b2cf5af120"
-"checksum hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "805026a5d0141ffc30abb3be3173848ad46a1b1664fe632428479619a3644d77"
 "checksum hex 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "023b39be39e3a2da62a94feb433e91e8bcd37676fbc8bea371daf52b7a769a3e"
 "checksum hostname 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "21ceb46a83a85e824ef93669c8b390009623863b5c195d1ba747292c0c72f94e"
 "checksum http 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)" = "d7e06e336150b178206af098a055e3621e8336027e2b4d126bda0bc64824baaf"
diff --git a/Cargo.toml b/Cargo.toml
index deaffa262..4171eb264 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,7 +11,7 @@ mmime = { version = "0.1.2", path = "./mmime" }
 
 libc = "0.2.51"
 pgp = { git = "https://github.com/rpgp/rpgp", branch = "master", default-features = false }
-hex = "0.3.2"
+hex = "0.4.0"
 sha2 = "0.8.0"
 rand = "0.6.5"
 smallvec = "0.6.9"
diff --git a/mmime/Cargo.toml b/mmime/Cargo.toml
index ddef4c84a..6a3bcadde 100644
--- a/mmime/Cargo.toml
+++ b/mmime/Cargo.toml
@@ -20,4 +20,4 @@ memmap = "0.7.0"
 lazy_static = "1.3.0"
 rand = "0.6.5"
 chrono = "0.4.6"
-hex = "0.3.2"
+hex = "0.4.0"