diff --git a/simulator/generation/plan.rs b/simulator/generation/plan.rs
index 028da2a30..9acef25ad 100644
--- a/simulator/generation/plan.rs
+++ b/simulator/generation/plan.rs
@@ -167,7 +167,7 @@ impl Display for Interaction {
     }
 }
 
-type AssertionFunc = dyn Fn(&Vec<ResultSet>, &SimulatorEnv) -> bool;
+type AssertionFunc = dyn Fn(&Vec<ResultSet>, &SimulatorEnv) -> Result<bool>;
 
 enum AssertionAST {
     Pick(),
@@ -375,12 +375,17 @@ impl Interaction {
                 unreachable!("unexpected: this function should only be called on assertions")
             }
             Self::Assertion(assertion) => {
-                if !assertion.func.as_ref()(stack, env) {
-                    return Err(limbo_core::LimboError::InternalError(
+                let result = assertion.func.as_ref()(stack, env);
+                match result {
+                    Ok(true) => Ok(()),
+                    Ok(false) => Err(limbo_core::LimboError::InternalError(
                         assertion.message.clone(),
-                    ));
+                    )),
+                    Err(err) => Err(limbo_core::LimboError::InternalError(format!(
+                        "{}. Inner error: {}",
+                        assertion.message, err
+                    ))),
                 }
-                Ok(())
             }
             Self::Assumption(_) => {
                 unreachable!("unexpected: this function should only be called on assertions")
@@ -404,12 +409,17 @@ impl Interaction {
                 unreachable!("unexpected: this function should only be called on assumptions")
             }
             Self::Assumption(assumption) => {
-                if !assumption.func.as_ref()(stack, env) {
-                    return Err(limbo_core::LimboError::InternalError(
+                let result = assumption.func.as_ref()(stack, env);
+                match result {
+                    Ok(true) => Ok(()),
+                    Ok(false) => Err(limbo_core::LimboError::InternalError(
                         assumption.message.clone(),
-                    ));
+                    )),
+                    Err(err) => Err(limbo_core::LimboError::InternalError(format!(
+                        "{}. Inner error: {}",
+                        assumption.message, err
+                    ))),
                 }
-                Ok(())
             }
             Self::Fault(_) => {
                 unreachable!("unexpected: this function should only be called on assumptions")
diff --git a/simulator/generation/property.rs b/simulator/generation/property.rs
index dd92a7af8..cae2a4145 100644
--- a/simulator/generation/property.rs
+++ b/simulator/generation/property.rs
@@ -1,3 +1,5 @@
+use limbo_core::LimboError;
+
 use crate::{
     model::{
         query::{Create, Delete, Insert, Predicate, Query, Select},
@@ -94,7 +96,7 @@ impl Property {
                     func: Box::new({
                         let table_name = insert.table.clone();
                         move |_: &Vec<ResultSet>, env: &SimulatorEnv| {
-                            env.tables.iter().any(|t| t.name == table_name)
+                            Ok(env.tables.iter().any(|t| t.name == table_name))
                         }
                     }),
                 });
@@ -109,8 +111,8 @@ impl Property {
                     func: Box::new(move |stack: &Vec<ResultSet>, _: &SimulatorEnv| {
                         let rows = stack.last().unwrap();
                         match rows {
-                            Ok(rows) => rows.iter().any(|r| r == &row),
-                            Err(_) => false,
+                            Ok(rows) => Ok(rows.iter().any(|r| r == &row)),
+                            Err(err) => Err(LimboError::InternalError(err.to_string())),
                         }
                     }),
                 });
@@ -131,7 +133,7 @@ impl Property {
                     message: "Double-Create-Failure should not be called on an existing table"
                         .to_string(),
                     func: Box::new(move |_: &Vec<ResultSet>, env: &SimulatorEnv| {
-                        !env.tables.iter().any(|t| t.name == table_name)
+                        Ok(!env.tables.iter().any(|t| t.name == table_name))
                     }),
                 });
 
@@ -147,10 +149,8 @@ impl Property {
                     func: Box::new(move |stack: &Vec<ResultSet>, _: &SimulatorEnv| {
                         let last = stack.last().unwrap();
                         match last {
-                            Ok(_) => false,
-                            Err(e) => e
-                                .to_string()
-                                .contains(&format!("Table {table_name} already exists")),
+                            Ok(_) => Ok(false),
+                            Err(e) => Ok(e.to_string().contains(&format!("Table {table_name} already exists"))),
                         }
                     }),
                 });