diff --git a/src/utils/importSQL/mariadb.js b/src/utils/importSQL/mariadb.js
index f7986fb51..f630928f8 100644
--- a/src/utils/importSQL/mariadb.js
+++ b/src/utils/importSQL/mariadb.js
@@ -56,7 +56,13 @@ export function fromMariaDB(ast, diagramDb = DB.GENERIC) {
             field.increment = false;
             if (d.auto_increment) field.increment = true;
             field.notNull = false;
-            if (d.nullable) field.notNull = true;
+            // `nullable` is a node for BOTH markers: `NULL` gives
+            // { type: "null" } and `NOT NULL` gives { type: "not null" },
+            // so testing it for truthiness marked an explicitly nullable
+            // column as NOT NULL. Only an omitted marker is undefined.
+            if (d.nullable && d.nullable.type !== "null") {
+              field.notNull = true;
+            }
             field.primary = false;
             if (d.primary_key) field.primary = true;
             field.default = "";
diff --git a/src/utils/importSQL/mssql.js b/src/utils/importSQL/mssql.js
index e9aea86db..09fc0482b 100644
--- a/src/utils/importSQL/mssql.js
+++ b/src/utils/importSQL/mssql.js
@@ -68,7 +68,13 @@ export function fromMSSQL(ast, diagramDb = DB.GENERIC) {
             field.increment = false;
             if (d.auto_increment) field.increment = true;
             field.notNull = false;
-            if (d.nullable) field.notNull = true;
+            // `nullable` is a node for BOTH markers: `NULL` gives
+            // { type: "null" } and `NOT NULL` gives { type: "not null" },
+            // so testing it for truthiness marked an explicitly nullable
+            // column as NOT NULL. Only an omitted marker is undefined.
+            if (d.nullable && d.nullable.type !== "null") {
+              field.notNull = true;
+            }
             field.primary = false;
             if (d.primary_key) field.primary = true;
             field.default = "";
diff --git a/src/utils/importSQL/mysql.js b/src/utils/importSQL/mysql.js
index 6bf06f7f2..318f2a1ee 100644
--- a/src/utils/importSQL/mysql.js
+++ b/src/utils/importSQL/mysql.js
@@ -56,7 +56,13 @@ export function fromMySQL(ast, diagramDb = DB.GENERIC) {
             field.increment = false;
             if (d.auto_increment) field.increment = true;
             field.notNull = false;
-            if (d.nullable) field.notNull = true;
+            // `nullable` is a node for BOTH markers: `NULL` gives
+            // { type: "null" } and `NOT NULL` gives { type: "not null" },
+            // so testing it for truthiness marked an explicitly nullable
+            // column as NOT NULL. Only an omitted marker is undefined.
+            if (d.nullable && d.nullable.type !== "null") {
+              field.notNull = true;
+            }
             field.primary = false;
             if (d.primary_key) field.primary = true;
             field.default = "";
diff --git a/src/utils/importSQL/postgres.js b/src/utils/importSQL/postgres.js
index ddee8b90b..a9df8db74 100644
--- a/src/utils/importSQL/postgres.js
+++ b/src/utils/importSQL/postgres.js
@@ -68,7 +68,13 @@ export function fromPostgres(ast, diagramDb = DB.GENERIC) {
             field.increment = false;
             if (d.auto_increment) field.increment = true;
             field.notNull = false;
-            if (d.nullable) field.notNull = true;
+            // `nullable` is a node for BOTH markers: `NULL` gives
+            // { type: "null" } and `NOT NULL` gives { type: "not null" },
+            // so testing it for truthiness marked an explicitly nullable
+            // column as NOT NULL. Only an omitted marker is undefined.
+            if (d.nullable && d.nullable.type !== "null") {
+              field.notNull = true;
+            }
             field.primary = false;
             if (d.primary_key) field.primary = true;
             field.default = "";
diff --git a/src/utils/importSQL/sqlite.js b/src/utils/importSQL/sqlite.js
index 51b4421ac..f6ce1dae0 100644
--- a/src/utils/importSQL/sqlite.js
+++ b/src/utils/importSQL/sqlite.js
@@ -131,7 +131,13 @@ export function fromSQLite(ast, diagramDb = DB.GENERIC) {
             field.increment = false;
             if (d.auto_increment) field.increment = true;
             field.notNull = false;
-            if (d.nullable) field.notNull = true;
+            // `nullable` is a node for BOTH markers: `NULL` gives
+            // { type: "null" } and `NOT NULL` gives { type: "not null" },
+            // so testing it for truthiness marked an explicitly nullable
+            // column as NOT NULL. Only an omitted marker is undefined.
+            if (d.nullable && d.nullable.type !== "null") {
+              field.notNull = true;
+            }
             field.primary = false;
             if (d.primary_key) field.primary = true;
             field.default = "";