diff --git a/src/main/java/com/bitpay/sdk/util/KeyUtils.java b/src/main/java/com/bitpay/sdk/util/KeyUtils.java
index c2f160a8..9b6d7c66 100644
--- a/src/main/java/com/bitpay/sdk/util/KeyUtils.java
+++ b/src/main/java/com/bitpay/sdk/util/KeyUtils.java
@@ -298,6 +298,12 @@ public static String sign(
         return result;
     }
 
+    private static boolean isHexDigit(char hex) {
+        return (hex >= '0' && hex <= '9')
+            || (hex >= 'A' && hex <= 'F')
+            || (hex >= 'a' && hex <= 'f');
+    }
+
     private static int getHexVal(char hex) {
         int val = hex;
         return val - (val < 58 ? 48 : (val < 97 ? 55 : 87));
@@ -321,7 +327,13 @@ public static byte[] hexToBytes(String hex) throws BitPayGenericException {
         byte[] arr = new byte[hex.length() >> 1];
 
         for (int i = 0; i < hex.length() >> 1; ++i) {
-            arr[i] = (byte) ((getHexVal(hexArray[i << 1]) << 4) + (getHexVal(hexArray[(i << 1) + 1])));
+            char high = hexArray[i << 1];
+            char low = hexArray[(i << 1) + 1];
+            if (!isHexDigit(high) || !isHexDigit(low)) {
+                BitPayExceptionProvider.throwGenericExceptionWithMessage(
+                    "Error: The binary key contains a non-hex digit");
+            }
+            arr[i] = (byte) ((getHexVal(high) << 4) + (getHexVal(low)));
         }
 
         return arr;
diff --git a/src/test/java/com/bitpay/sdk/util/KeyUtilsTest.java b/src/test/java/com/bitpay/sdk/util/KeyUtilsTest.java
index 563ff4d1..3a4592eb 100644
--- a/src/test/java/com/bitpay/sdk/util/KeyUtilsTest.java
+++ b/src/test/java/com/bitpay/sdk/util/KeyUtilsTest.java
@@ -6,6 +6,7 @@
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 
 import com.bitpay.sdk.exceptions.BitPayGenericException;
@@ -46,6 +47,11 @@ public void it_should_convert_hex_to_bytes() throws BitPayGenericException {
     assertArrayEquals(expectedBytes, actualBytes);
   }
 
+  @Test
+  public void it_should_reject_a_non_hex_key_digit() {
+    assertThrows(BitPayGenericException.class, () -> KeyUtils.hexToBytes("0G"));
+  }
+
   @Test
   public void it_should_convert_bytes_to_hex() {
     byte[] bytes = { 1, 35, 69, 103, -119, -85, -51, -17 };