diff --git a/.changeset/nine-bugs-drop.md b/.changeset/nine-bugs-drop.md
new file mode 100644
index 00000000000..1a01ed5b311
--- /dev/null
+++ b/.changeset/nine-bugs-drop.md
@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+fix(er): recognize '1' cardinality alias before relationship operators
diff --git a/cypress/integration/rendering/erDiagram.spec.js b/cypress/integration/rendering/erDiagram.spec.js
index 542de9f24a9..ad811f02aae 100644
--- a/cypress/integration/rendering/erDiagram.spec.js
+++ b/cypress/integration/rendering/erDiagram.spec.js
@@ -471,4 +471,30 @@ ORDER ||--|{ LINE-ITEM : contains
       { logLevel: 1, flowchart: { htmlLabels: false } }
     );
   });
+
+  it('should render ER diagram with "1" cardinality alias before relationship operators', () => {
+    imgSnapshotTest(
+      `
+      erDiagram
+        CUSTOMER 1--1 ORDER : "exactly one"
+        ORDER 1--o{ LINE-ITEM : "one to many"
+        PRODUCT 1--|{ CATEGORY : "one or more"
+        USER 1..1 PROFILE : "exactly one optional"
+      `,
+      { logLevel: 1 }
+    );
+  });
+
+  it('should render ER diagram with "1" cardinality using all 4 relationship operator styles', () => {
+    imgSnapshotTest(
+      `
+      erDiagram
+        A 1--1 B : "solid-solid"
+        C 1..1 D : "dotted-dotted"
+        E 1.-1 F : "dotted-solid"
+        G 1-.1 H : "solid-dotted"
+      `,
+      { logLevel: 1 }
+    );
+  });
 });
diff --git a/packages/mermaid/src/diagrams/er/parser/erDiagram.jison b/packages/mermaid/src/diagrams/er/parser/erDiagram.jison
index f581c6777fa..89a797b50a6 100644
--- a/packages/mermaid/src/diagrams/er/parser/erDiagram.jison
+++ b/packages/mermaid/src/diagrams/er/parser/erDiagram.jison
@@ -68,6 +68,7 @@ accDescr\s*"{"\s*                                { this.begin("acc_descr_multili
 "only one"                      return 'ONLY_ONE';
 [0-9]+\.[0-9]+                  return 'DECIMAL_NUM';
 "1"(?=\s+[A-Za-z_"'])           return 'ONLY_ONE';
+"1"(?=(\-\-|\.\.|\.\-|\-\.))    return 'ONLY_ONE';
 "1"                             return 'ENTITY_ONE';
 [0-9]+                          return 'NUM';
 \|\|                            return 'ONLY_ONE';
diff --git a/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js b/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js
index 05948988d92..39a042e526d 100644
--- a/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js
+++ b/packages/mermaid/src/diagrams/er/parser/erDiagram.spec.js
@@ -734,6 +734,52 @@ describe('when parsing ER diagram it...', function () {
     expect(rels[0].relSpec.cardB).toBe(erDb.Cardinality.ZERO_OR_MORE);
   });
 
+  it('should handle "1" alias directly followed by identifying relationship operator "--"', function () {
+    erDiagram.parser.parse('erDiagram\nCUSTOMER 1--one or more DELIVERY-ADDRESS : has');
+    const rels = erDb.getRelationships();
+
+    expect(erDb.getEntities().size).toBe(2);
+    expect(rels.length).toBe(1);
+    expect(rels[0].relSpec.cardA).toBe(erDb.Cardinality.ONE_OR_MORE);
+    expect(rels[0].relSpec.cardB).toBe(erDb.Cardinality.ONLY_ONE);
+    expect(rels[0].relSpec.relType).toBe(erDb.Identification.IDENTIFYING);
+  });
+
+  it('should handle "1" alias directly followed by non-identifying relationship operator ".."', function () {
+    erDiagram.parser.parse('erDiagram\nCUSTOMER 1..one or more DELIVERY-ADDRESS : has');
+    const rels = erDb.getRelationships();
+
+    expect(erDb.getEntities().size).toBe(2);
+    expect(rels.length).toBe(1);
+    expect(rels[0].relSpec.cardA).toBe(erDb.Cardinality.ONE_OR_MORE);
+    expect(rels[0].relSpec.cardB).toBe(erDb.Cardinality.ONLY_ONE);
+    expect(rels[0].relSpec.relType).toBe(erDb.Identification.NON_IDENTIFYING);
+  });
+
+  it('should handle "1" alias directly followed by mixed relationship operator ".-"', function () {
+    erDiagram.parser.parse('erDiagram\nCUSTOMER 1.-one or more DELIVERY-ADDRESS : has');
+    const rels = erDb.getRelationships();
+
+    expect(erDb.getEntities().size).toBe(2);
+    expect(rels.length).toBe(1);
+    expect(rels[0].relSpec.cardA).toBe(erDb.Cardinality.ONE_OR_MORE);
+    expect(rels[0].relSpec.cardB).toBe(erDb.Cardinality.ONLY_ONE);
+    // ".-" is dotted-to-solid, which is NON_IDENTIFYING on the left side
+    expect(rels[0].relSpec.relType).toBe(erDb.Identification.NON_IDENTIFYING);
+  });
+
+  it('should handle "1" alias directly followed by mixed relationship operator "-."', function () {
+    erDiagram.parser.parse('erDiagram\nCUSTOMER 1-.one or more DELIVERY-ADDRESS : has');
+    const rels = erDb.getRelationships();
+
+    expect(erDb.getEntities().size).toBe(2);
+    expect(rels.length).toBe(1);
+    expect(rels[0].relSpec.cardA).toBe(erDb.Cardinality.ONE_OR_MORE);
+    expect(rels[0].relSpec.cardB).toBe(erDb.Cardinality.ONLY_ONE);
+    // "-." is solid-to-dotted, which is NON_IDENTIFYING per the grammar
+    expect(rels[0].relSpec.relType).toBe(erDb.Identification.NON_IDENTIFYING);
+  });
+
   it('should represent identifying relationships properly', function () {
     erDiagram.parser.parse('erDiagram\nHOUSE ||--|{ ROOM : contains');
     const rels = erDb.getRelationships();