diff --git a/README.md b/README.md
index c90c711..d4c7707 100644
--- a/README.md
+++ b/README.md
@@ -77,6 +77,7 @@ make it work with JUnit 5. Feel free to use the code (in package ```de.platon42.
 - Cosmetics: Changed Register Flow Documentation wording from _reads_ to _uses_ and from _modifies_ to _changes_.
 - Bugfix: Minor fix for `andi/eori/ori to ccr` which were not byte sized in ISA.
 - Bugfix: Added alternate condition code tests `HS (=CC)` and `LO (=CS)`.
+- Performance: Optimized mnemonic lookup.
 
 ### V0.4 (03-Aug-21)
 
diff --git a/build.gradle b/build.gradle
index 2bfe217..889afa6 100644
--- a/build.gradle
+++ b/build.gradle
@@ -63,6 +63,7 @@ patchPluginXml {
       <li>Cosmetics: Changed Register Flow Documentation wording from 'reads' to 'uses' and from 'modifies' to 'changes'.
       <li>Bugfix: Minor fix for `andi/eori/ori to ccr` which were not byte sized in ISA.
       <li>Bugfix: Added alternate condition code tests HS (=CC) and LO (=CS).
+      <li>Performance: Optimized mnemonic lookup.
     </ul>
   <h4>V0.4 (03-Aug-21)</h4>
     <ul>
diff --git a/src/main/java/de/platon42/intellij/plugins/m68k/asm/M68kIsa.kt b/src/main/java/de/platon42/intellij/plugins/m68k/asm/M68kIsa.kt
index 23744b9..0497c69 100644
--- a/src/main/java/de/platon42/intellij/plugins/m68k/asm/M68kIsa.kt
+++ b/src/main/java/de/platon42/intellij/plugins/m68k/asm/M68kIsa.kt
@@ -1002,29 +1002,19 @@ object M68kIsa {
         )
     )
 
-    val mnemonics =
-        isaData.asSequence()
-            .flatMap {
-                if (it.conditionCodes.isEmpty()) it.altMnemonics.plus(it.mnemonic) else it.altMnemonics.plus(it.conditionCodes
-                    .map { cc ->
-                        it.mnemonic.replace("CC", cc)
-                    })
-            }
-            .toSet()
+    private val mnemonicLookupMap = isaData.asSequence()
+        .flatMap {
+            (if (it.conditionCodes.isEmpty()) it.altMnemonics.plus(it.mnemonic) else it.altMnemonics.plus(it.conditionCodes
+                .map { cc ->
+                    it.mnemonic.replace("CC", cc)
+                })).map { mnemonic -> mnemonic to it }
+        }
+        .groupBy({ it.first }) { it.second }
+
+    val mnemonics = mnemonicLookupMap.keys
 
     fun findMatchingInstructions(mnemonic: String): List<IsaData> {
-        val lowerMnemonic = mnemonic.lowercase()
-        return isaData
-            .filter {
-                if (it.conditionCodes.isEmpty()) {
-                    (it.mnemonic == lowerMnemonic) || it.altMnemonics.any { altMnemonic -> altMnemonic == lowerMnemonic }
-                } else {
-                    it.altMnemonics.any { altMnemonic -> altMnemonic == lowerMnemonic } ||
-                            it.conditionCodes.any { cc ->
-                                it.mnemonic.replace("CC", cc) == lowerMnemonic
-                            }
-                }
-            }
+        return mnemonicLookupMap.getOrDefault(mnemonic.lowercase(), emptyList())
     }
 
     fun findMatchingOpMode(candidates: List<IsaData>, op1: AddressMode?, op2: AddressMode?, opSize: Int?, specialReg: String?): List<IsaData> {