diff --git a/src/main/java/org/mariadb/jdbc/MariaDbBlob.java b/src/main/java/org/mariadb/jdbc/MariaDbBlob.java
index 15bb3fcf3..7ae67203c 100644
--- a/src/main/java/org/mariadb/jdbc/MariaDbBlob.java
+++ b/src/main/java/org/mariadb/jdbc/MariaDbBlob.java
@@ -83,7 +83,7 @@ public MariaDbBlob() {
      */
     public MariaDbBlob(byte[] bytes) {
         if (bytes == null) {
-            throw new AssertionError("byte array is null");
+            throw new NullPointerException("byte array is null");
         }
         data = bytes;
         offset = 0;
@@ -99,7 +99,7 @@ public MariaDbBlob(byte[] bytes) {
      */
     public MariaDbBlob(byte[] bytes, int offset, int length) {
         if (bytes == null) {
-            throw new AssertionError("byte array is null");
+            throw new NullPointerException("byte array is null");
         }
         data = bytes;
         this.offset = offset;
diff --git a/src/main/java/org/mariadb/jdbc/MariaDbClob.java b/src/main/java/org/mariadb/jdbc/MariaDbClob.java
index a23a059d3..1fbd1fcf1 100644
--- a/src/main/java/org/mariadb/jdbc/MariaDbClob.java
+++ b/src/main/java/org/mariadb/jdbc/MariaDbClob.java
@@ -55,6 +55,7 @@
 import org.mariadb.jdbc.internal.util.exceptions.ExceptionMapper;
 
 import java.io.*;
+import java.nio.charset.CharacterCodingException;
 import java.nio.charset.StandardCharsets;
 import java.sql.Clob;
 import java.sql.NClob;
@@ -97,11 +98,7 @@ public MariaDbClob() {
      * @return string value of blob content.
      */
     public String toString() {
-        try {
-            return new String(data, offset, length, StandardCharsets.UTF_8);
-        } catch (Exception e) {
-            throw new AssertionError(e);
-        }
+        return new String(data, offset, length, StandardCharsets.UTF_8);
     }
 
     /**
@@ -192,7 +189,7 @@ private int utf8Position(int charPosition) {
             if (byteValue < 0x80) {
                 pos += 1;
             } else if (byteValue < 0xC2) {
-                throw new AssertionError("invalid UTF8");
+                throw new UncheckedIOException("invalid UTF8",new CharacterCodingException());
             } else if (byteValue < 0xE0) {
                 pos += 2;
             } else if (byteValue < 0xF0) {
@@ -200,7 +197,7 @@ private int utf8Position(int charPosition) {
             } else if (byteValue < 0xF8) {
                 pos += 4;
             } else {
-                throw new AssertionError("invalid UTF8");
+                throw new UncheckedIOException("invalid UTF8",new CharacterCodingException());
             }
         }
         return pos;
@@ -239,7 +236,7 @@ public long length() {
             if (byteValue < 0x80) {
                 i += 1;
             } else if (byteValue < 0xC2) {
-                throw new AssertionError("invalid UTF8");
+                throw new UncheckedIOException("invalid UTF8",new CharacterCodingException());
             } else if (byteValue < 0xE0) {
                 i += 2;
             } else if (byteValue < 0xF0) {
@@ -247,7 +244,7 @@ public long length() {
             } else if (byteValue < 0xF8) {
                 i += 4;
             } else {
-                throw new AssertionError("invalid UTF8");
+                throw new UncheckedIOException("invalid UTF8",new CharacterCodingException());
             }
             len++;
         }
@@ -262,7 +259,7 @@ public void truncate(final long len) throws SQLException {
             if (byteValue < 0x80) {
                 pos += 1;
             } else if (byteValue < 0xC2) {
-                throw new AssertionError("invalid UTF8");
+                throw new UncheckedIOException("invalid UTF8",new CharacterCodingException());
             } else if (byteValue < 0xE0) {
                 pos += 2;
             } else if (byteValue < 0xF0) {
@@ -270,7 +267,7 @@ public void truncate(final long len) throws SQLException {
             } else if (byteValue < 0xF8) {
                 pos += 4;
             } else {
-                throw new AssertionError("invalid UTF8");
+                throw new UncheckedIOException("invalid UTF8",new CharacterCodingException());
             }
         }
         length = pos - offset;
diff --git a/src/main/java/org/mariadb/jdbc/MariaDbDatabaseMetaData.java b/src/main/java/org/mariadb/jdbc/MariaDbDatabaseMetaData.java
index 5bf491afa..ce174850d 100644
--- a/src/main/java/org/mariadb/jdbc/MariaDbDatabaseMetaData.java
+++ b/src/main/java/org/mariadb/jdbc/MariaDbDatabaseMetaData.java
@@ -399,7 +399,7 @@ private static int getImportedKeyAction(String actionKey) {
                 return DatabaseMetaData.importedKeyRestrict;
 
             default:
-                throw new AssertionError("should not happen");
+                throw new IllegalArgumentException("Illegal key action '" + actionKey + "' specified.");
         }
     }
 
diff --git a/src/main/java/org/mariadb/jdbc/internal/com/send/gssapi/StandardGssapiAuthentication.java b/src/main/java/org/mariadb/jdbc/internal/com/send/gssapi/StandardGssapiAuthentication.java
index 104769e95..f49396b77 100644
--- a/src/main/java/org/mariadb/jdbc/internal/com/send/gssapi/StandardGssapiAuthentication.java
+++ b/src/main/java/org/mariadb/jdbc/internal/com/send/gssapi/StandardGssapiAuthentication.java
@@ -92,7 +92,7 @@ public void authenticate(final PacketOutputStream writer, final String serverPri
                 }
                 jaasConfFile.deleteOnExit();
             } catch (final IOException ex) {
-                throw new IOError(ex);
+                throw new UncheckedIOException(ex);
             }
 
             System.setProperty("java.security.auth.login.config", jaasConfFile.getCanonicalPath());