diff --git a/core/resources/l10n/messages.properties b/core/resources/l10n/messages.properties
index 2844bd5b6..0abbc4f4a 100644
--- a/core/resources/l10n/messages.properties
+++ b/core/resources/l10n/messages.properties
@@ -1414,6 +1414,7 @@ RASAeroExport.error29 = Boattail length may not be zero.
 RASAeroExport.error30 = Boattail rear diameter may not be zero.
 RASAeroExport.error31 = Stage '%s' can only contain a body tube (incl. shoulder transition), ignoring other %d component(s).
 RASAeroExport.error32 = Boattails can only be added to the last stage.
+RASAeroExport.error33 = Invalid component '%s' in sustainer stage.
 
 ! SaveAsFileChooser
 SaveAsFileChooser.illegalFilename.title = Illegal filename
diff --git a/core/src/net/sf/openrocket/file/rasaero/export/RocketDesignDTO.java b/core/src/net/sf/openrocket/file/rasaero/export/RocketDesignDTO.java
index 1b6fe6367..c9dd0c63b 100644
--- a/core/src/net/sf/openrocket/file/rasaero/export/RocketDesignDTO.java
+++ b/core/src/net/sf/openrocket/file/rasaero/export/RocketDesignDTO.java
@@ -113,6 +113,8 @@ public class RocketDesignDTO {
                     } else {
                         addExternalPart(new TransitionDTO((Transition) component, warnings, errors));
                     }
+                } else {
+                    throw new RASAeroExportException(String.format(trans.get("RASAeroExport.error33"), component.getComponentName()));
                 }
             } catch (RASAeroExportException e) {
                 errors.add(e.getMessage());